After the firefight in the gas pipes area near the exit point of the map, 
there will be a gas pipe on fire. Turn the
object off in the next room, then return to the now extinguished pipe 
area..There is a semi secret walkway
there. Walk in, find the ladder, and climb up. You will find a health 
booster, and there is a door on your left.
Go into that office. Listen to the song. It is the main theme from Shogo: 
Mobile Armor Division, an anime
FPS created by Mololith. Look at the dry marker board. It is the same one 
from an office level in Shogo:
Mobile Armor Division.