In particular, 100 meters is definitely not acceptable, and the mountain is 100 meters, usurping the role of the host.
The mountain should be flat and low. It looks like a table in a cave. If you need to look up, it is unlucky to be uneven.
To tell the truth, there are very few caves with mountains. It's hard to find a cave with a backer, a hall and a dragon and tiger sand ... A cave with a mountain above the hall is the real dragon cave. So what you describe should not be mountains ... you have misunderstood the concept.