The niche gets the corner treatment as well. Like the drain, this is a staple of the old school CRPGs, and many a D&D dungeon. Like with the drain, the corner pieces can be mixed and matched with any others to create unique corner pieces. Here we see the niche on both sides, and the right and left, along with the eroded and block floor textures.
I've included an update to the wall niche pieces as well, because the floor for niches needs to have a carve out, so I've also added support for the block texture there as well, and attached those here.
Grab the files