It sure is.

Nah, they're pretty chill. I go down there at least 2-3x a week for work stuff. I've never had to give a reason for going down there past "going to building [x]". Hell, you may get lucky and they might just buzz you in without ever saying anything.

I forgot about that part one day. I had my sun-roof open and it had rained the day before. Water was still coming from that opening and I drove right under it getting water all in my car. Not a lot, but enough to make me question my intelligence.

If you want to go down there and just drive around, you can. Go down the Kearney entrance, there is an intercom right before you go in, hit the button. Security is going to answer, they usually just say something like "Underground Security" or "which building are you going to?". It really doesn't matter what the guard says, just say "Going to building 9" (you can use other buildings too, but that is just the building I go to the most so I say that) and they'll open the gate.

You obviously can't go inside any of the warehouses, but you can sort of just drive around down there if you want. Going later in the afternoon is probably easier because there is less trucks down there so there is less you have to watch out for. It's pretty cool to just look at imo.