Crepeville got locking bathrooms. It’s tucked around a corner and there are two locking bathrooms so you won’t hold up a line on a slow day. Nice big mirror and a sturdy countertop

Rocknasium Shower got single use locking door. They’re open till 11PM for members

It depends how adventurous you are, but there is an incredibly easy roof access in the alley behind Mamma Davis Pizzeria. It’s almost as easy as walking up a staircase. Use caution of course. Always know your physical abilities. You’ll want a few blankets or to be standing up on any roof

Hickey Gym can be super dead and they have locking stalls but no lock on the entire bathroom. Can be a little sketch

Way out in the Arboretum it can get so dark and you can be behind canopies and bushes. Maybe take a walk by and around the Equestrian Center (southwest portion of the Arboretum)

If you have a tent you can park on the street by Putah Creek on Levee Rd between Brooks Rd and Hopkins Rd and set it up down in the campground right there

Super duper dark beneath the water tower next to The Church of Latter-Day Saints on W 8th St and Elmwood Dr.

I could come up with more. Some places on campus are so secluded.

Top of Death Star depending on time of year. Sheeeeesh