When I was in college, I got fucked in a botanical garden after hours by a security guard. Very atmospheric.
My ex also had me suck him off in the car on a long road trip, parked at in an empty church parking lot. He also tried to fuck me in a random shady bar bathroom in the French Quarter of New Orleans, but that felt a little too scary.
In a church was probably the most interesting. My girlfriend at the time was there doing something for her mom and I swung by after work. Everyone left us alone in the backroom to go grab something. Neither she nor I were particularly religious, and we thought it would be fun to blasphemy a little.