Darn. Why mayas only? You've got some nice stuff going on. The modeling repetition will make for nice shadows in lighting, painting textures will make it more dynamic. For instance, this place is underground. Are there leaks in the ceiling, that during a heavy rain, drip and discolor it? If so, the spot underneath the leak could be discolored as well. And maybe it's raining outside now, so there's a bucket there! Give it a character, a story. You may not want to build a jail that is just a jail, you may want it to be alive. Have fun with it.