As a teen, I explored this place 3 times and got busted on the third time, so never went back.
Preston Castle aka the Preston "School of Industry" (Ione, CA)
It was a home for juvenile delinquents. Who knows what kind of fucked up "corrective measures" they did there in the late 1800s up until it was abondoned in 1960.
It was creepy as hell but nothing too crazy happened. There was a juvenile vulture nesting in one of the closets which was weird.
Fun fact: country legend Merle Haggard went there (and escaped more than once). He and my grandfather grew up in the same area (Oildale/Bakersfield) and my grandpa taught his son in high school.