I'm looking for a square mesh that already might exist in the CS that I can use to create a seamless or at least somewhat seamless functional cube-room that a player can be inside and thereby open up the possibility of creating series' of rooms composed of such makeshift cubes. It would be nice if such a thing already existed, though, if it does not, I may try my hand at creating this myself.

edit:
I've discovered that in_t_l_room_floor suits my needs, but the piece has 6 faces which is more than I'd like. Is it possible for a square piece to have 1 face, or am I misunderstanding the term?

There are a few:

In_Lava_Blacksquare
in_lava_256
in_lava_256a
in_lava_512
in_lava_1024
in_lava_1024_01
terrain_bc_scum_01
terrain_bc_scum_02
terrain_bc_scum_03

That's great, thank you!