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A recessed wall or pop-up wall is a tile in Chip's Challenge that acts as a wall to everything except Chip. Chip can only step on it once, after which it becomes a wall. The level Cellblocked is composed exclusively of recessed walls.
In Chip's Challenge 1, similarly to many other items under removable tiles, recessed walls will not take effect if revealed under these tiles. The second step on the recessed wall will be the one that turns it into a wall. Also, if a block is on top of a recessed wall, Chip can enter the square while revealing the tile as a wall.