I have a set of Jurassic Park mines for my old server, JurassicPrison. You may have seen them or stopped by the server. If you haven't I will be happy to send some images.

One time I dug (or, rather, blew with TNT) a huge cavern deep underground and filled the ground with lava and built a huge volcano prison inside, using nether bricks building material. I'd show you some screenshots if i still had it, but it turned out pretty cool in the end