I'll put in my two cents since no one else has responded. I haven't done it in a couple years but I believe its called Amigos Wreck. Its a bit of a swim from the bouy and is only a small tug boat I believe. The dive masters usually bring a chumsicle and you get to see sharks, large groupers and big eels. Its great for a change of pace from the reef dives. All dive shops go there, you will just need to ask them in advance so they can reserve other people who are interested in going as well. Again, my info is a couple years old so thing may have changed.