This looks sweet!

[segundo3000gt]

I went a couple of years ago with Seaya Diving.  The guide provides you information about what you're going to see on your dive to give you a better idea what you're looking at.  The mine is divided into a bunch of "caverns", though I use the word caverns loosely because there are no enclosed areas that you can't ascend to the surface.  The guide primarily leads you from one cavern to the next along a series of pre-planned paths they've set up but you have freedom to look around at whatever intrigues you in each area.  I remember visibility being about as good as any dive I've done in the Caribbean.  I plan to head back at some point and I would recommend it.