The first floor is composed of three solid stone floors, and one stone floor with stairwell hole in the NNW corner (representing access to the tunnel below the keep). A door sits in the SSE corner (a double door centered between the first floor walls is impossible with the current Dwarven Forge pieces). Piled on the floor are pieces of ruined stone wall.
Two foamboard pieces are stuck to the floor with poster tack and serve as supports for the 3rd floor and 4th floor. Without them, the unsupported floors had a tendency to sag.