The Matrix is a virtual world, which exists only inside the computer. This is a simulation of the World as it was in the 1990s, and there are millions of people living in this world. They do the same as we did back in the 1990s. Following that logic its obvious that they have bars, telefone dealers, and show caves. Unfortunately we could not find a single reference of a show cave, show mine, or subterranea in the vast literature which was written about The Matrix.
On the other side there is an underground structure outside the Matrix, so we listed this site. We hope you will be kind enough to overlook the fact that, strictly speaking, it is not in The Matrix.