For more details, see http://grim-fandango.wikia.com/wiki/Department_of_Death
Also, I always thought that the hidden elevator (spoiler warning) in the pavement in the alley behind the DoD was a contrived idea that someone made up just for the game. But these are actually common in San Francisco - see the last picture. They are used to bring stuff in from delivery trucks in the street directly to the basement level of buildings (e.g. hotels), take out garbage, etc.
Now go play the game again. What are you waiting for? https://www.gog.com/game/grim_fandango_remastered
And while you're at it, go get Day Of The Tentacle (Remastered) as well! https://www.gog.com/game/day_of_the_tentacle_remastered