Schools, Colleges, Campuses; I can’t say I am a great fan of this type of explore. These places are BIG and take some exploring. I like to get in and out before anyone notices. If you are arsing around for 2-3 hours, then security may turn up.
I would not say abandoned education facilities are in short supply, but you need to get in before they demolish them. Schools tend to not make great renovation projects and wiping them from existence once abandoned appears to be becoming more commonplace.