Shadowy floor fills room 11/1; if stepped on, non-Shadows or those not specially treated like Shadow Puppets are risk sinking through it into a shadow plane or the Mirrorbound Archive. Echoes of what the room was still exist - scaffolding, pallets of building supplies, and the battle-damaged and broken shell of a Bound Elemental, all as shadow forms. The door to the room is also an echo, as is much of the connecting hall's walls.
You can tell I am well into the floor, because I've had to write a reminder to add stairs to my map.
