Press "~" to bring up the console then type "map " and than the following to go to any map.

Effect	Code
ATV map	jungle2
Darwin evolution map	area57
First jungle (mountain gorge)	jungle
First sewer level	sewera
Second sewer levels	sewerb
Sinclaire estate	estate
The oil rig	oilrig
Thrall master	thral
Xenomorphic lab	lab1 or lab
Xenomorphic study	lab2 or study