As the only mess hall on site, the grand mess hall provides for all staff. Seating a few hundred at maximum capacity on steel furniture that really digs into your ass, the mess provides food that is free, inoffensive, and filling. The chefs must have been imported from america too.
Psi-7's favorite room by time spent, medical is exactly as you'd expect. The medical wing is nearby the labs, and has near-direct access from the loading bay. It contains surgical and recuperative facilities, nurses and doctors who are considerably more interested in your health than your happiness, and a pathological level of cleanliness maintained at all times. If the doctor knows you by name and you've never actually had a conversation, then that's a bad sign and you should probably stop trying to block bullets with your face.
Anywhere you have a bunch of physical types, you will find a place for them to lift things. The gym is large and well outfitted, with various weights, bags and machines for the cultivation of a healthy state of being. It's located nearby to the dorms, though not so close as to disturb anyone's rest. The most notable feature is the full-size boxing ring, where agents can punch and kick each other to their hearts' content. People tend to stick humorous notes on the punching bags representing things they'd very much like to hit, although "Gillepsie" has yet to be seen.
The gun range is exactly what you would expect. It's located down below the gym, in a large arched room. Although only inert projectiles are permitted to be used, there is a wide selection of such weapons available for use, along with the appropriate safety equipment. There are facilities allowing weapons to be shot by those who would not be permitted to take a weapon with them around the site.
Up on the top of the mountain, accessible via an outside foot trail or an interior elevator, is the observatory. It is a large, domed structure, on par with what might be seen at a very serious astronomical facility. It's used primarily for spacial monitoring, though there are some telescopes available for stargazing.