On the backroom (where there is Red Armor and Mega Health) there is a teleport that goes to the main (BIG) room of the map.
If you jump just before the teleport and "aim" your jump so you go in the top left corner of the teleport, you'll get stuck inside the teleport but not go through until you move a bit.
Also, staying stuck for too long on that teleport during a game, will drown your player, which should definitely confuse your opponent as there is no water deep enough to drown players on DM2.
Good times! Long live QuakeWorld!
I was really confused when I hit that.
Alternatively you can download nQuake [1], a full pack with most things included except for the non-shareware maps. You can then just place the pak1.pak file inside the id1 folder and make it complete.
Good luck ;)