I guess some ridiculous percentage of people get certified to go on one vacation and never dive again. Silly.
Anyway,
-- Night/limited visibility diving
-- Boat diving
-- Dry suit
-- Navigation
Then a couple more dives after that to reach 25 and we're "advanced", whatever that means.
But yeah, scuba's still fun. We went around and (partially) into a sunken amphibious personnel carrier last weekend, and I found a golfball (Titleist! anyone here a Marine biologist!?) and a Gilligan hat.