Two places spring to mind, both with my ex...

1) On the stairs, 20 floors up in a block of flats (apartment building)

2) In a cubicle of a communal public swimming pool in Paris (France) on our honeymoon... no (real) risk of getting caught, but it was fun hearing people walk by while we were doing it.. with her trying her best to keep quiet - she managed too.... just!!

__________________
The selfish, they're all standing in line
Faithing and hoping to buy themselves time
Me, I figure as each breath goes by
I only own my mind