Down

tap a wall. now it is the floor.

a glass box of sand and three blocks: tap any wall and it becomes the floor, and everything loose pours toward it

Down is not a property of the world, it is a direction the world happens to agree on, and here you get to overrule it. Tap any wall of the box and gravity turns to face it: the sand pours sideways until it rests against the wall you chose, and the blocks tumble after it and knock on their new floor. Nothing about the sand knows which wall is the bottom; the same rule that piles it on the floor piles it on the ceiling, because a floor is only the wall things fall toward. The room does not turn with you, which is why the light on the blocks stays where it was and only the shadow moves.

Concepts: gravity, physics.

An interactive you play with one thumb, on Wundr.