The other major tournament at Royal Troon
The southernmost end of the championship course at Royal Troon directly abuts a trailer park, called the Prestwick Holiday Park -- which also separates Troon from Prestwick Golf Club.
In fact, the trailer park is so close to the course that when you tee off on the tenth hole you practically hang your rear end over the fence. (In both the U.K. and Ireland, a surprising amount of what looks to an American like prime seaside real estate is occupied by mobile homes and RVs.)
A Troon member once told me that another Troon member, while traveling, overheard some other diners in a restaurant discussing a recent tournament at Troon and eagerly went over to introduce himself. It turned out that the tournament they were discussing was an event conducted surreptitiously by golf-playing residents of the trailer park, on the Troon holes nearest their caravans -- including the Postage Stamp, which I played in 2009 (in neither the Open Championship nor the Prestwick Holiday Park Invitational):