A Map that is completely made of rock. The up build limit is very small, but the map is very deep. You dig underground, make a big cavern, and people can make houses out of the rock. I do this in other servers and it is very fun, but I wish there was a dedicated server.
Also, if anyone knows a map that is a Falling Lava server (http://minecraftwiki.net/wiki/Server) can you tell me? It seems fun.