Chemical weathering is one way we get caverns. When water infiltrates the pore spaces in limestone, chemical weathering may occur and a cavern can form. Chemical weathering due to the formation of acid and then the subsequent acid precipitation can cause buildings and statues made of limestone and marble as well as natural rock formations to chemically weather. Certain metals like iron for instance, can react with oxygen and form iron oxide, which is the rust you see on old fences.
Chemical weathering happens when chemical reactions happen that break down the bonds that hold rocks together. There are many types of reactions that can cause chemical weathering. The most common are oxidation, hydrolysis and carbonation.
Carbonation, for example, happens when carbon dioxide in water forms carbonic acid and then reacts with the minerals in the rock.
The phenomenon of chemical weathering takes place in almost all types of rocks but it's much more common in locations where there is plenty of water.
Why is that?
Since we know that chemical weathering is the chemical phenomenon where the bonds that are holding the rocks together are broken down by chemical reactions, then it is easy to explain why chemical weathering is happening in places with a lot of water.
We know that presence of water makes most of the chemical reactions to take place so, chemical weathering is happening easier when the water is around.