A few years ago I had the pleasure of spending 10 weeks in hospital, which as well as having bits dating back to 1860 and being extended every couple of decades, is also attached to the local uni. The only way I stayed sane was spending my nights exploring as much as I could, made all the more exciting by having to crawl up stairs and drag my wheelchair behind me. I decided very quickly that "no public access" signs didn't apply as I wasn't a member of the public, I was an inpatient.

Elevators are particularly interesting. You might need a key-card to get onto the 4th floor, but it turns out that for efficiency half the elevators waited on that top floor. Get into elevator, read book for 5 minutes, wait for it to reset, go home and let you out in the restricted section. Or this entire floor is locked off from the stairway, but the floor above is open and the elevator lets me go down a floor and get out.

It's honestly amazing where you can end up, especially if you combine boredom, time and a bit of a can-do attitude. One of my favourite games was using the stick from an ice-lolly (sold from a machine in reception) to jimmy the lock on badly fitted doors. I also found an ebay pair of scrubs to be really useful once I'd worked out how to get into places - you'd go down a corridor, have people stick their heads out of doors and start with "Hey! You can't be down her---oh sorry doctor". I ended up reporting most of it to security just after I got released. They refused to engage, but had swapped out all the locks when I had a check-up a year later.