diff --git a/TODO.md b/TODO.md
index 600e787..e448b58 100644
--- a/TODO.md
+++ b/TODO.md
@@ -32,4 +32,10 @@ if inpututil.IsKeyJustPressed(ebiten.KeyS) {
   velocity and  included snap in so  that the player ends  up right on
   the edge of the obstacle and not inside as it is now
   
-- Check player-player collisions! 
+- Check player-player collisions!
+
+- Do all collision detections in ONE system
+
+- do not use the map anymore for collision detection
+
+- check swept AABB instead of my collision detection, to allow for higher speeds
diff --git a/assets/levels/00-deadly-obstacles.lvl b/assets/levels/00-deadly-obstacles.lvl
index 710e398..41dafbc 100644
--- a/assets/levels/00-deadly-obstacles.lvl
+++ b/assets/levels/00-deadly-obstacles.lvl
@@ -4,7 +4,7 @@ Background: background-lila
                     
                     
    #######          
-   #     #          
+   #o    #          
    #  t  #          
    #> S <#          
    #     #          
diff --git a/assets/levels/04-mayhem.lvl b/assets/levels/04-mayhem.lvl
index db2966d..52353b9 100644
--- a/assets/levels/04-mayhem.lvl
+++ b/assets/levels/04-mayhem.lvl
@@ -4,13 +4,13 @@ Background: background-lila
                     
                     
                     
-     ##########     
-    #         v#    
+     ########W#     
+    #     v    #    
     #          #    
     #S        s#    
-    #          #    
-    #^         #    
-     ##########     
+    ############    
+    # o        #    
+     ######## #     
                     
                     
                     
diff --git a/assets/loader-levels.go b/assets/loader-levels.go
index f75ec09..5defb2a 100644
--- a/assets/loader-levels.go
+++ b/assets/loader-levels.go
@@ -25,18 +25,42 @@ type Tile struct {
 	Id          byte
 	Sprite      *ebiten.Image
 	Class       string
-	Solid       bool
-	Player      bool
-	IsPrimary   bool
-	Renderable  bool
-	Velocity    bool
-	Collectible bool
-	Transient   bool
-	Particle    int // -1=unused, 0-3 = show image of slice
-	Tiles       []*ebiten.Image
-	TileNames   []string // same thing, only the names
-	Obstacle    bool
-	Direction   int // obstacles
+	Solid       bool            // wall brick
+	Player      bool            // player sphere
+	IsPrimary   bool            // primary player sphere
+	Renderable  bool            // visible, has sprite
+	Velocity    bool            // movable
+	Collectible bool            // collectible, vanishes once collected
+	Transient   bool            // turns into brick wall when traversed
+	Destroyable bool            // turns into empty floor when bumped into twice
+	Particle    int             // -1=unused, 0-3 = show image of slice
+	Tiles       []*ebiten.Image // has N sprites
+	TileNames   []string        // same thing, only the names
+	Obstacle    bool            // is an obstacle/enemy
+	Direction   int             // obstacle business end shows into this direction
+}
+
+func (tile *Tile) Clone() *Tile {
+	newtile := &Tile{
+		Id:          tile.Id,
+		Sprite:      tile.Sprite,
+		Class:       tile.Class,
+		Solid:       tile.Solid,
+		Player:      tile.Player,
+		IsPrimary:   tile.IsPrimary,
+		Renderable:  tile.Renderable,
+		Velocity:    tile.Velocity,
+		Collectible: tile.Collectible,
+		Transient:   tile.Transient,
+		Destroyable: tile.Destroyable,
+		Particle:    tile.Particle,
+		Tiles:       tile.Tiles,
+		TileNames:   tile.TileNames,
+		Obstacle:    tile.Obstacle,
+		Direction:   tile.Direction,
+	}
+
+	return newtile
 }
 
 const (
@@ -128,7 +152,7 @@ func NewTileTranswall(class []string) *Tile {
 	}
 
 	return &Tile{
-		Id:         '*',
+		Id:         't',
 		Class:      "transwall",
 		Solid:      false,
 		Renderable: true,
@@ -139,6 +163,27 @@ func NewTileTranswall(class []string) *Tile {
 	}
 }
 
+func NewTileHiddenDoor(class []string) *Tile {
+	sprites := []*ebiten.Image{}
+	names := []string{}
+
+	for _, sprite := range class {
+		sprites = append(sprites, Assets[sprite])
+		names = append(names, sprite)
+	}
+
+	return &Tile{
+		Id:          'W',
+		Class:       "hiddendoor",
+		Solid:       false,
+		Renderable:  true,
+		Destroyable: true,
+		Tiles:       sprites,
+		Sprite:      sprites[0], // initially use the first
+		TileNames:   names,
+	}
+}
+
 // used to map level data bytes to actual tiles
 type TileRegistry map[byte]*Tile
 
@@ -164,7 +209,8 @@ type RawLevel struct {
 func InitTiles() TileRegistry {
 	return TileRegistry{
 		' ': {Id: ' ', Class: "floor", Renderable: false},
-		'#': NewTileBlock("block-grey32"),
+		//'#': NewTileBlock("block-grey32"),
+		'#': NewTileBlock("block-greycolored"),
 		'B': NewTileBlock("block-orange-32"),
 		'S': NewTilePlayer(Primary),
 		's': NewTilePlayer(Secondary),
@@ -183,6 +229,7 @@ func InitTiles() TileRegistry {
 			"particle-ring-6",
 		}),
 		't': NewTileTranswall([]string{"transwall", "block-orange-32"}),
+		'W': NewTileHiddenDoor([]string{"block-greycolored", "block-greycolored-damaged"}),
 	}
 }
 
diff --git a/assets/sprites/block-greycolored-damaged.png b/assets/sprites/block-greycolored-damaged.png
new file mode 100644
index 0000000..aa9df25
Binary files /dev/null and b/assets/sprites/block-greycolored-damaged.png differ
diff --git a/assets/sprites/block-greycolored.png b/assets/sprites/block-greycolored.png
new file mode 100644
index 0000000..a72c4d0
Binary files /dev/null and b/assets/sprites/block-greycolored.png differ
diff --git a/components/destroyable.go b/components/destroyable.go
new file mode 100644
index 0000000..f29f375
--- /dev/null
+++ b/components/destroyable.go
@@ -0,0 +1,29 @@
+package components
+
+import (
+	"log"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+// A hidden door in a wall. If the player bumps into it once, it shows
+// damage and it vanishes the next time.
+
+type Destroyable struct {
+	Activated bool
+	Sprites   []*ebiten.Image
+	Current   int // sprite index
+}
+
+func (door *Destroyable) GetNext() *ebiten.Image {
+	if len(door.Sprites) > door.Current {
+		door.Current++
+		return door.Sprites[door.Current]
+	}
+
+	log.Fatalf("not enough sprites in transient tile, have %d sprites, index requested: %d",
+		len(door.Sprites), door.Current+1,
+	)
+
+	return nil
+}
diff --git a/game/game.go b/game/game.go
index b75ca31..ba16f05 100644
--- a/game/game.go
+++ b/game/game.go
@@ -96,7 +96,6 @@ func (game *Game) Update() error {
 
 		if next == Play {
 			// fresh setup of actual level every time we enter the play scene
-			//game.Scenes[Play] = NewLevelScene(game, gameobserver.CurrentLevel)
 			game.Scenes[Play].SetLevel(gameobserver.CurrentLevel)
 		}
 
diff --git a/game/levels.go b/game/levels.go
index 69e7047..4cb52e8 100644
--- a/game/levels.go
+++ b/game/levels.go
@@ -3,6 +3,7 @@ package game
 import (
 	"image"
 	"log"
+	"log/slog"
 	"openquell/assets"
 	"openquell/components"
 	"openquell/grid"
@@ -15,12 +16,16 @@ import (
 	"github.com/mlange-42/arche/ecs"
 )
 
+type Map map[image.Point]*assets.Tile
+type BackupMap map[image.Point]assets.Tile
+
 type Level struct {
 	Cellsize, Width, Height int
 	World                   *ecs.World
 	Name                    string
 	Description             string
-	Mapslice                map[image.Point]*assets.Tile
+	Mapslice                Map
+	BackupMapslice          Map
 	GridContainer           *grid.GridContainer
 	Systems                 []systems.System
 	Grid                    *grid.Grid
@@ -45,16 +50,21 @@ func NewLevel(game *Game, cellsize int, plan *assets.RawLevel) *Level {
 
 	systemlist = append(systemlist, systems.NewTransientSystem(game.World, gridcontainer))
 
+	systemlist = append(systemlist, systems.NewDestroyableSystem(game.World, gridcontainer))
+
+	mapslice, backupmap := LevelToSlice(game, plan, cellsize)
+
 	return &Level{
-		Mapslice:      LevelToSlice(game, plan, cellsize),
-		Cellsize:      cellsize,
-		World:         game.World,
-		Width:         game.ScreenWidth,
-		Height:        game.ScreenHeight,
-		Description:   plan.Description,
-		Name:          plan.Name,
-		GridContainer: gridcontainer,
-		Systems:       systemlist,
+		Mapslice:       mapslice,
+		BackupMapslice: backupmap,
+		Cellsize:       cellsize,
+		World:          game.World,
+		Width:          game.ScreenWidth,
+		Height:         game.ScreenHeight,
+		Description:    plan.Description,
+		Name:           plan.Name,
+		GridContainer:  gridcontainer,
+		Systems:        systemlist,
 	}
 }
 
@@ -77,6 +87,12 @@ func (level *Level) Position2Point(position *components.Position) image.Point {
 	}
 }
 
+func (level *Level) RestoreMap() {
+	for point, tile := range level.BackupMapslice {
+		level.Mapslice[point] = tile.Clone()
+	}
+}
+
 func (level *Level) SetupGrid(game *Game) {
 	// generic variant does not work here:
 	// selector := generic.NewFilter1[components.Position]()
@@ -92,15 +108,20 @@ func (level *Level) SetupGrid(game *Game) {
 	playerobserver := observers.GetPlayerObserver(level.World)
 	playerobserver.RemoveEntities()
 
+	// get rid of possibly manipulated map
+	level.RestoreMap()
+
 	// setup world
+	slog.Debug("new grid?")
 	level.GridContainer.SetGrid(
 		grid.NewGrid(game.World, level.Cellsize, level.Width, level.Height, level.Mapslice))
 }
 
 // parses a RawLevel and generates a mapslice from it, which is being used as grid
-func LevelToSlice(game *Game, level *assets.RawLevel, tilesize int) map[image.Point]*assets.Tile {
+func LevelToSlice(game *Game, level *assets.RawLevel, tilesize int) (Map, Map) {
 	size := game.ScreenWidth * game.ScreenHeight
-	mapslice := make(map[image.Point]*assets.Tile, size)
+	mapslice := make(Map, size)
+	backupmap := make(Map, size)
 
 	for y, line := range strings.Split(string(level.Data), "\n") {
 		if len(line) != game.ScreenWidth/tilesize && y < game.ScreenHeight/tilesize {
@@ -113,9 +134,11 @@ func LevelToSlice(game *Game, level *assets.RawLevel, tilesize int) map[image.Po
 				log.Fatalf("unregistered tile type %c encountered", char)
 			}
 
-			mapslice[image.Point{x, y}] = assets.Tiles[byte(char)]
+			tile := assets.Tiles[byte(char)]
+			mapslice[image.Point{x, y}] = tile
+			backupmap[image.Point{x, y}] = tile.Clone()
 		}
 	}
 
-	return mapslice
+	return mapslice, backupmap
 }
diff --git a/grid/grid.go b/grid/grid.go
index 7870f96..5c6edc1 100644
--- a/grid/grid.go
+++ b/grid/grid.go
@@ -61,12 +61,18 @@ func NewGrid(world *ecs.World,
 		components.Renderable,
 		components.Transient](world)
 
+	doormapper := generic.NewMap3[
+		components.Position,
+		components.Renderable,
+		components.Destroyable](world)
+
 	var pos *components.Position
 	var vel *components.Velocity
 	var render *components.Renderable
 	var speed *components.Speed
 	var transient *components.Transient
 	var player *components.Player
+	var destroyable *components.Destroyable
 
 	playerobserver := observers.GetPlayerObserver(world)
 	obstacleobserver := observers.GetObstacleObserver(world)
@@ -99,6 +105,10 @@ func NewGrid(world *ecs.World,
 				entity := transmapper.New()
 				pos, render, transient = transmapper.Get(entity)
 				transient.Sprites = tile.TileNames
+			case tile.Destroyable:
+				entity := doormapper.New()
+				pos, render, destroyable = doormapper.Get(entity)
+				destroyable.Sprites = tile.Tiles
 			default:
 				log.Fatalln("unsupported tile type encountered")
 			}
@@ -143,7 +153,15 @@ func (grid *Grid) GetTile(
 	return tile
 }
 
-func (grid *Grid) SetTile(tile *assets.Tile, point image.Point) {
+func (grid *Grid) RemoveTile(point image.Point) {
+	delete(grid.Map, point)
+}
+
+func (grid *Grid) SetFloorTile(point image.Point) {
+	grid.Map[point] = assets.Tiles[' ']
+}
+
+func (grid *Grid) SetSolidTile(tile *assets.Tile, point image.Point) {
 	solidmapper := generic.NewMap4[
 		components.Position,
 		components.Renderable,
diff --git a/src/block-grey-damage.xcf b/src/block-grey-damage.xcf
new file mode 100644
index 0000000..728eb2d
Binary files /dev/null and b/src/block-grey-damage.xcf differ
diff --git a/src/block-grey.xcf b/src/block-grey.xcf
index 7d4da3d..4f11d52 100644
Binary files a/src/block-grey.xcf and b/src/block-grey.xcf differ
diff --git a/systems/destroyable_system.go b/systems/destroyable_system.go
new file mode 100644
index 0000000..45db9b3
--- /dev/null
+++ b/systems/destroyable_system.go
@@ -0,0 +1,108 @@
+package systems
+
+import (
+	"log/slog"
+	"openquell/components"
+	. "openquell/components"
+	. "openquell/config"
+
+	"openquell/grid"
+	"openquell/observers"
+
+	"github.com/hajimehoshi/ebiten/v2"
+	"github.com/mlange-42/arche/ecs"
+	"github.com/mlange-42/arche/generic"
+)
+
+type DestroyableSystem struct {
+	World         *ecs.World
+	Selector      *generic.Filter3[Position, Renderable, Destroyable]
+	GridContainer *grid.GridContainer
+	SolidMapper   generic.Map4[ // needed for replacement
+		components.Position,
+		components.Renderable,
+		components.Tilish,
+		components.Solid]
+}
+
+type DoorToRemove struct {
+	Entity   ecs.Entity
+	Position *components.Position
+}
+
+func NewDestroyableSystem(world *ecs.World, gridcontainer *grid.GridContainer) System {
+	solidmapper := generic.NewMap4[
+		components.Position,
+		components.Renderable,
+		components.Tilish,
+		components.Solid](world)
+
+	system := &DestroyableSystem{
+		Selector:      generic.NewFilter3[Position, Renderable, Destroyable](),
+		World:         world,
+		GridContainer: gridcontainer,
+		SolidMapper:   solidmapper,
+	}
+
+	return system
+}
+
+func (system *DestroyableSystem) Update() error {
+	playerobserver := observers.GetPlayerObserver(system.World)
+	posID := ecs.ComponentID[components.Position](system.World)
+	veloID := ecs.ComponentID[components.Velocity](system.World)
+
+	query := system.Selector.Query(system.World)
+
+	EntitiestoRemove := []*DoorToRemove{}
+
+	for query.Next() {
+		doorposition, renderable, door := query.Get()
+
+		for player := range playerobserver.Entities {
+			playerposition := (*Position)(system.World.Get(player, posID))
+			playervelocity := (*Velocity)(system.World.Get(player, veloID))
+
+			ok, newpos := doorposition.Intersects(playerposition, playervelocity)
+			if ok {
+				// player bumped into hidden wall, activate it, snap in player
+				slog.Debug("bump not die", "originalpos", playerposition)
+				playervelocity.Change(Stop)
+				playerposition.Set(newpos)
+
+				if door.Activated {
+					// player bumps into the door a second time, now hide it
+					EntitiestoRemove = append(EntitiestoRemove,
+						&DoorToRemove{Entity: query.Entity(), Position: doorposition})
+				} else {
+					slog.Debug("activating destroyable", "doorpos", doorposition)
+					door.Activated = true
+					renderable.Image = door.GetNext()
+				}
+			}
+		}
+	}
+
+	for _, door := range EntitiestoRemove {
+		slog.Debug("hiding destroyable", "doorpos", door.Position.Point())
+
+		// remove door entity
+		system.World.RemoveEntity(door.Entity)
+	}
+
+	return nil
+}
+
+func (system *DestroyableSystem) Draw(screen *ebiten.Image) {
+	// write transients (these are no tiles!)
+	op := &ebiten.DrawImageOptions{}
+	query := system.Selector.Query(system.World)
+
+	for query.Next() {
+		pos, render, _ := query.Get()
+
+		op.GeoM.Reset()
+		op.GeoM.Translate(float64(pos.X), float64(pos.Y))
+		screen.DrawImage(render.Image, op)
+	}
+}
diff --git a/systems/grid_system.go b/systems/grid_system.go
index ffcda72..495a1f6 100644
--- a/systems/grid_system.go
+++ b/systems/grid_system.go
@@ -3,6 +3,7 @@ package systems
 import (
 	"image"
 	"image/draw"
+	"log/slog"
 	. "openquell/components"
 
 	"github.com/hajimehoshi/ebiten/v2"
@@ -44,8 +45,8 @@ func (system *GridSystem) Update() error { return nil }
 func (system *GridSystem) Draw(screen *ebiten.Image) {
 	op := &ebiten.DrawImageOptions{}
 	query := system.Selector.Query(system.World)
-
 	if !system.UseCache || query.Count() != system.Count {
+		slog.Debug("entity number changes", "old", system.Count, "current", query.Count())
 		// map not cached or cacheable, write it to the cache
 		draw.Draw(system.Cache, system.Background.Bounds(), system.Background, image.ZP, draw.Src)
 
@@ -54,6 +55,7 @@ func (system *GridSystem) Draw(screen *ebiten.Image) {
 		for query.Next() {
 			sprite, pos, _ := query.Get()
 
+			//slog.Debug("drawing sprite", "sprite", sprite, "point", pos.Point())
 			draw.Draw(
 				system.Cache,
 				image.Rect(pos.X, pos.Y, pos.X+pos.Cellsize, pos.Y+pos.Cellsize),
diff --git a/systems/transient_system.go b/systems/transient_system.go
index 1a03437..5e4bcc0 100644
--- a/systems/transient_system.go
+++ b/systems/transient_system.go
@@ -95,7 +95,7 @@ func (system *TransientSystem) Update() error {
 
 		//  also  setup the  grid  tile  with  a  new solid,  so  that
 		// collision detection works
-		system.GridContainer.Grid.SetTile(
+		system.GridContainer.Grid.SetSolidTile(
 			assets.NewTileBlock(convertible.NewSprite),
 			convertible.Position.Point(),
 		)