Oooh... I just found a skywalking one in cs_assault. From the main gate of the warehouse, above the little hut is a ledge, you can place a baby behind an invis wall there, and get to the other side of the warehouse, jump up on buildings, get to the highest point and jump into the streets. Bam, skywalking. You can also get into the tunnels on either side of the traintracks, though they dont go very far. On another note, you can jump onto the building directly right of zombie spawn, get to the top and make your way to the fence part, from there you can put a baby on top of a vent and get out of the map on zombie side. Not much there really, but if a kind... err make that mischievious stalker master decides to send a human over, he should be able to be far enough away from warghouls to grab some achievments.