Some courses are so good, so blessed with great architecture, that they can't make room for a brilliant little par-3 on their main 18-hole routing. But, thankfully, they don't discard the holes altogether, instead keeping them either as "bye" (or bet-settling) holes or, especially in Australia, as maintenance breathers for the main course. (Question for Aussies in the know: Were the extra holes on the Sandbelt courses built with maintenance in mind, or was maintenance simply a fortuitous byproduct of their retention?) Whatever the correct nomenclature, they are what I call the best extra holes in golf.
My nominations, obviously limited by the courses I've played, are below. (I also remember fondly the extra hole at Metropolitan Golf Club, routed between the 5th and 6th holes, but we played through another group on that hole, so I unfortunately have no pictures of it.) Please share yours, preferably with a picture if you have one. Happy Sunday.
Cruden Bay's 19th (routed between the 12th and 13th holes)
Kingston Heath's 19th (routed between the 1st and 2nd holes)
Barnbougle Lost Farm's 19th (routed between the 13th and 14th holes; note that Lost Farm also has a 20th hole, which comes after the 18th on the way to the clubhouse)
Barnbougle Lost Farm's 19th (front-right tee)
Royal Melbourne Composite's 19th (just as the Composite Course itself isn't legitimate as a standalone entity, neither is this hole, as it's the 16th hole--i.e., not an extra--of the club's East Course, but it is rotated with the East's 4th hole in serving as the 16th hole for the Composite Course, so I figured including it on this list had some merit; if it were a legitimate "extra" hole, I'd place it at the top of this list, it's so good)