Our guide would turn on lights as we went along, and then turn off the lights in the passages we had just come through. At one point he turned off all the lights and let us experience the most complete darkness I have ever felt. We entered the caverns down through a stairway locked with iron gates in a little stone building, and exited up a different stairway into the basement of the main building. The entering and exiting was one of my favourite parts of the experience. It is just so surreal to feel that transition from everyday reality to the strange and magical world underground.
(I think it's kind of hilarious how much this picture looks like it should be in a brochure)