I have no idea what would qualify, as the most unique place I've had sex with someone.
I mean how do I choose amongst the following unique places (some with my wife, some not)?
I had sex with my ex-wife for the first time, at a party in a lounge room with other friends in the room (and our friends saw and heard it all), through the night, a couple of hours after we met.
I've had sex on a tabletop tennis, table top.
I've had sex in a monorail going around a city CBD.
I've had sex in the open at various parks, and some tourist attraction lookouts.
I've had sex on the entrance to a walking track at a mountain attraction on a very foggy night (with my wife), and we got the "hmmm, hmmm", when some random bush walker came out of nowhere, so we stopped briefly and carried on once he had passed.
I've had sex during a lunch break, in a random apartment complex entrance stairwell. We couldn't wait so we went for it.
I've had sex on some random persons home driveway one night.
I've had sex standing up (somewhat inebriated) on a dance floor in the middle of other dancing patrons, in a nightclub. And funnily enough after that, on the way home in a bus, another woman took a fancy to me and I had sex with her on the following day.
I've had sex in the open on a few beaches, including a nudist beach.
I've had sex on some mountain tops or very near the top in other instances.
I've had sex in the open, at a university, near one of their experimental sites (and like @so_sweet
my wife got bitten by mosquitos on her bare behind a lot).
I've had sex in, on and against different cars, at some rest stops and parking spots.
I've had sex on the floor with one woman, in the bedroom of a mutual woman friend while she was sleeping on her bed.
I've had sex in a tent while camping.
I've had sex in a tent at a party.
I've had sex in a coastal gun emplacement.
I've had sex on a lookout picnic table.
I've had sex in some caves.
I've had sex in some random wilderness locations.
I've had sex in some streets and alleyways , including in a few city CBD's.
I've had sex on some jetty's, and under some bridges.
And I just remembered I've had sex in a cemetery, and on the grounds of some church on one occasion, and a couple of train stations as well.