Scale model for a space with a large skylight (or courtyard or roof garden or balcony). The room is constructed around the skylight. It has a reflective floor and walls which slope outwards.
The reflective floor mirrors the sky and extends the sky below.
Walls slope outwards so that one sees only the sky and not one's own reflection. In a small room, viewers sit in the center of the room.
The shape of room is circular to evoke a planetarium (more ideal), or hexagonal/triangular/rectangular (easier to construct).