How did you manage to get to those places?
A select few know a VERY well hidden glitch involving the Zepplin, in which can Teleport you instantly to anywhere you wish. (I assume they need to edit a file before logging on.)
They do it without hacking or using 3rd party programs. (Hacking as in, modifying the data stream, switching files around, etc. And 3rd party programs as in those ones that modify data and confuse the server to teleport you places.)
I know a little bit of how it's done, but haven't quite figured it out yet. (I only attempt to do so on the test server, as most of the time, they really don't care as long as you're quiet about it. The last test realm was moderated, and one dude who likes to push his limits with GMs got banned for a day for going to GM Island and announcing it everywhere. =P)
They can transport others to these places by using Mind Control on a Priest on you in a duel. Anyway, the trick takes effect once you jump off the Zepplin, and then you get transported to another map.
Don't ask me how it works, I only have slight clues on how it's done. Don't bother asking them either, they won't tell you because they don't want Blizzard fixing it.
Anyway, that place I refer to as a "Holodeck" is embedded in the Mountain of GM Island, behind the house.
And yes, DarkNecrid, there used to be glitch involving boats and using fear in a duel to get to GM Island, and Outlands. The glitch involved being on the top part of the boat on those little wooden plank things (I forget what they're called right now, I suck at boat knowledge. =P) and then you'd stand on the edge. You'd get a lock or a priest friend to duel you, and once feared, you'd go CRAZY FAST through the world in a certain direction. You'd eventually hit "Outlands" (Which has been taken out as of 1.10) and you'd /forfiet the duel to "land" (Somehow, you're still considered next to the person while going crazy fast through the world's terrian I guess.)