Volcaninc Chamber

As you follow the long tunnel downwards, the air gets warmer. Eventually the floor and walls are noticeably hot to the touch. You must be very deep now. Soon, you emerge into a tall, narrow room with cracked and craggy walls.

There are three cracks that look big enough for you to pass through. One is narrow, one is just wide enough to walk through, and the last is so wide you would have to stretch your arms out to touch both sides at once.