Now, if this question doesn't wake up this list nothing will.
Best sex I ever had was on the beach just as dawn and a lunar eclipse met over the Juan de Fuca straight. Early birds, a coast guard patrol and some dude walking his dogs were the only witnesses.
First sex of the relationship and a special astronomical moment.
Was awesome.

And then there was sex on the balcony for the neighbours on the upper floors of the next building. You can't beat exhibitionism for an aphrodisiac. lol.