A large pile of stones between Masham and Leeds UK, where lovers under time pressure rendezvous for sexual encounters, usually in a car. Not as creepy as a "dogging" location. But definitely more freaky than "Lookout Point" after the prom in an American movie.
"Got t' kids tonight luv. Quickie at t' Slag Heap after work?"
"Happy St. Patrick's Day. Would you like to celebrate it with me at the Slag Heap?"
"Horny as fuck. Wanna get Hulk Smashed behind the Slag Heap."
When particularly busy and text messages must be kept brief:
"Slag Heap?"