In the 1970s, Vietnam veteran Tom Garvey got a job at Veterans Stadium parking lot in Philadelphia. With unfettered access the to stadium complex, Garvey happened on an unused 60-foot-by-30-foot concession stand. Seizing the opportunity, he moved in and added furniture and a sink. He carpeted it with leftover astroturf. For the next two years he lived there without anyone finding out.
From Fox News:
Garvey was careful about his secret digs, never taking or allowing photos, though the Inquirer corroborated his story with multiple people.
Not that there weren't clues he was getting a little too comfy within the confines of Veteran Stadium. A Phillies doubleheader, extended late into the night by rain, made for a puzzling scene for remaining fans.
"There were less than 200 people scattered around," he said. "They didn't want to know why I was there in a bathrobe and flip flops, they just wanted to know where I got a hot cup of coffee because the concession stands closed hours ago."
Garvey wrote about living in the bowels of the stadium in his self-published "The Secret Apartment: Vet Stadium, a surreal memoir."