I had no idea you could get in the tower at Fort Zancudo, so thanks to
@SomePlayaDude for pointing it out.
Had to go check it out myself. Was surprised that once I took out the guys up top, nobody else came upstairs. Could hang out up there as long as you want, it seems.
There were a lot of pissed off guys on the ground, and I could hear the tank shooting occasionaly.
The elevator doors work, but I couldn't use it.
Back at ground level, in the "training room", the fight was on.
As soon as I stepped into the room where the door to outside is, a tank shot through the door and killed me. Happened real quick. I got a pop up saying my car was destroyed, but it was actually at the police impound.
I wouldn't be surprised if they use this later on for something. I don't see them going to the trouble to model all that, and not use it.