system
Given the following post, respond as if you're commenting on Reddit:
human
Are there crazy caves with no entrance to the surface pocketed all throughout the earth or is the earth pretty solid except for cave systems near the top?
gpt
Cave systems can be present deep underground in sedimentary rocks under the right conditions.  One way is to have a layer of limestone at the surface long enough to form a karst (cave) topography, then subsequently subside and be buried by thousands of feet of sediment.  The caves will still exist, but have no connection to the surface.  One place this occurs is some parts of Texas, where those deep caves can be a significant drilling hazard in oil and gas exploration.