The AC Maple Leaf Lounge at YQR (Regina) is slightly larger than a broom closet...about 15'x20', self service accessed with a keycode given at the check-in counter.
I also recall a similarly tiny lounge at Fiji International operated by CPAir back in the days when its DC10s stopped to refuel between AKL/SYD and HNL. (Actually don't think it was as much a refueling stop as an opportunity to have us roam the Duty Free shop, back in the 80s offering the best prices in the world, though passengers were also dropped off and picked up from this vacation paradise before the revolution.)