Here are just some sketches, coming up with more ideas, experimenting with different shapes. Not compositions for painting.
Testing different shaped walls.
Here is another different look where the walls are slightly curved and leaning over, giving a sort of claustrophobic feeling.
For the pit I've tried to focus on drawing some rats. hopefully slightly better than before.
Here are just a few more sketches of the pit at different angles.
For this last picture, I've come up with the idea of a close up on the pendulum with the rest of the picture of the pit in it's reflection.