diff --git a/js/format-c2m.js b/js/format-c2m.js
index 820ac84..2883907 100644
--- a/js/format-c2m.js
+++ b/js/format-c2m.js
@@ -203,7 +203,7 @@ const TILE_ENCODING = {
     0x8a: 'thief_keys',
     // 0x8b: Ghost : '#direction', '#next'
     // 0x8c: Steel foil : '#next'
-    0x8d: ['turtle', 'water'],
+    0x8d: 'turtle',
     // 0x8e: Secret eye : '#next'
     // 0x8f: Thief bribe : '#next'
     // 0x90: Speed boots : '#next'
diff --git a/js/main.js b/js/main.js
index b3a1c49..d641b2e 100644
--- a/js/main.js
+++ b/js/main.js
@@ -544,7 +544,8 @@ class Level {
         if (goal_x >= 0 && goal_x < this.width && goal_y >= 0 && goal_y < this.height) {
             // Check for a thin wall in our current cell first
             for (let tile of original_cell) {
-                if (tile !== actor && tile.type.thin_walls &&
+                if (tile !== actor &&
+                    ! tile.type.is_swivel && tile.type.thin_walls &&
                     tile.type.thin_walls.has(direction))
                 {
                     blocked = true;
diff --git a/js/tileset.js b/js/tileset.js
index e77d582..2f4a9d4 100644
--- a/js/tileset.js
+++ b/js/tileset.js
@@ -189,7 +189,11 @@ export const CC2_TILESET_LAYOUT = {
         west: [[9, 12], [10, 12], [11, 12]],
     },
     foil: [12, 12],
-    turtle: [13, 12],  // TODO also 14 + 15 for sinking
+    turtle: {
+        // Turtles draw atop fake water, but don't act like water otherwise
+        overlay: [13, 12],  // TODO also 14 + 15 for sinking
+        base: 'water',
+    },
 
     walker: [0, 13],
     // TODO walker animations span multiple tiles, rgh
diff --git a/js/tiletypes.js b/js/tiletypes.js
index c374850..31183a1 100644
--- a/js/tiletypes.js
+++ b/js/tiletypes.js
@@ -88,18 +88,54 @@ const TILE_TYPES = {
     swivel_ne: {
         draw_layer: LAYER_OVERLAY,
         thin_walls: new Set(['north', 'east']),
+        is_swivel: true,
+        on_depart(me, level, other) {
+            if (other.direction === 'north') {
+                level.transmute_tile(me, 'swivel_se');
+            }
+            else if (other.direction === 'east') {
+                level.transmute_tile(me, 'swivel_nw');
+            }
+        },
     },
     swivel_se: {
         draw_layer: LAYER_OVERLAY,
         thin_walls: new Set(['south', 'east']),
+        is_swivel: true,
+        on_depart(me, level, other) {
+            if (other.direction === 'south') {
+                level.transmute_tile(me, 'swivel_ne');
+            }
+            else if (other.direction === 'east') {
+                level.transmute_tile(me, 'swivel_sw');
+            }
+        },
     },
     swivel_sw: {
         draw_layer: LAYER_OVERLAY,
         thin_walls: new Set(['south', 'west']),
+        is_swivel: true,
+        on_depart(me, level, other) {
+            if (other.direction === 'south') {
+                level.transmute_tile(me, 'swivel_nw');
+            }
+            else if (other.direction === 'west') {
+                level.transmute_tile(me, 'swivel_se');
+            }
+        },
     },
     swivel_nw: {
         draw_layer: LAYER_OVERLAY,
         thin_walls: new Set(['north', 'west']),
+        is_swivel: true,
+        on_depart(me, level, other) {
+            if (other.direction === 'north') {
+                level.transmute_tile(me, 'swivel_ne');
+            }
+            else if (other.direction === 'west') {
+                level.transmute_tile(me, 'swivel_ne');
+            }
+        },
     },
 
     // Locked doors
@@ -186,8 +222,11 @@ const TILE_TYPES = {
         },
     },
     turtle: {
-        // XXX well not really because it goes on top of water??
         draw_layer: LAYER_TERRAIN,
+        on_depart(me, level, other) {
+            // TODO become a splash (good test: push a block on a turtle, then push again; you don't fall in water because the splash blocks you!)
+            level.transmute_tile(me, 'water');
+        },
     },
     ice: {
         draw_layer: LAYER_TERRAIN,