According to wikipedia,

A reality hacker is an urban spelunker. "Building hacker" is a better term than "reality hacker" for participants in urban exploration activity. Using the definition of hacker that the mainstream media uses, a reality hacker is like a computer hacker but instead of hacking into computers, a reality hacker "hacks" (enters without authorization, trespasses, explores) in real life.

This reminds me a chapter of "The Happy Mutant Handbook" by Simon Garfield (Building Hacker). The author explained the pleasure of discovering new places or new way to manipulate the surroundings. He also gave tips.