A rock shelter is also called a rock house or crepuscular cave. It is a shallow cave-like opening at the base of a bluff or cliff. Many rock shelters are found under waterfalls. They form natural shelters from the weather. If you have found a rock shelter and have decided to stay in it, building a small fire in the mouth of the shelter and a reflector behind it is the safest way to stay warm. Building the fire inside a rock shelter will heat the roof and can cause slabs to spall off, causing a hazard. You can also build low walls around the entrance to rock shelters to act both as a reflector and a windbreak.