How caves look like?

Dark, very darK! :-)

They have certain classes of passage morphology, especially cross-sections, due to their detail mode of formation. The walls have textures related to the specific rock and chemical weathering regime that formed them. All these details are valuable in assessing how the particular cave developed.

They can be "active" - carrying the stream still carrying them. They can be "fossil" or "abandoned" - left high and dry by losing their formative streams, and these especially may present large heaps of fallen boulders, sand-banks, rich masses of stalactites and stalagmites, etc.

The "passage" may be a vertical shaft, which may or may not open to the surface, and many of these are very impressive indeed.

Each cave is unique.