What makes passages in caves?

Most caves are in limestone, and their passagesare active or former stream-courses, the cavities themsleves having formed primarily by weakly-acidic rain water dissolving the limestone.

It takes tens or hundreds of thousands of years to do so. I think a rate of lowering or rock surface for a cave stream in Carboniferous Limestone in temperate climates can be around 2 or 3mm/100yrs.

There are other cave types such asLava Tubes, from molten rockrunning out from under a solidified crust, and Mass-Movement Fissures, which are a land-slip feature.