I've explored Treasure Island quite a bit over the past couple years, documenting the remains.
The basement of Bldg 1 seems mostly unused these days, and is VERY spooky. There are a couple SCIFs, the Fleet Admiral Chester Nimitz Briefing Theater, a walk-in vault, and then a section that looks like it might have been a small hospital or infirmary, in addition to a variety of plain looking office type rooms.
I'd love to learn from some of you what these Bldg 1 basement facilities were actually used for during whatever era you were assigned to NAVSTA TI.