Start a new single-player game. After the Boot Camp level is done loading, do not click the "Next" icon. Instead, press ~ to display the console window. Type remoteaccess 1 to enable remote access, then type LOGIN developer to enable cheat mode. Enter loadscenario("umc_spscenario1","") using one of the following level names. When the new level is done loading the console window will disappear. Click the "Next" icon to start the new level.

bootcamp
cube
vertigo
brooklynsp
illegal
station
warehousesp
tucson
border
mansion
house
haunted
temple
gothic
space
plant
deadend