General terms:
* Cavern: This is a synonym for cave, often used for larger or more impressive caves.
* Grotto: This usually refers to a smaller cave, often with beautiful or ornate features.
* Hollow: This can refer to a cave, but also to any other kind of depression in the ground.
* Shelter: This emphasizes the function of a cave as a place of protection.
Specific terms:
* Shaft: This refers to a vertical cave entrance.
* Passage: This refers to a long, narrow corridor within a cave.
* Chamber: This refers to a large, open space within a cave.
* Stalactite/Stalagmite: These are specific formations found in caves.
Figurative terms:
* Abyss: This is a metaphorical term for a deep, dark cave, often used to represent something unknown or dangerous.
* Den: This refers to a cave that is used as a home by animals.
The best noun to use will depend on the specific situation. For example, if you are talking about a large, impressive cave, "cavern" would be a good choice. If you are talking about a small, sheltered cave, "grotto" might be more appropriate.