a membership at the 'gym' = a 'gym' membership
Students are required to take 'gym'.
He works out at the 'gym'.
(..) I hate it when they move in Iike that. Mia, it's not a championship game. It's not even a big game. It's just gym cIass. Just hit the baII. I don't want to fIunk you in gym cIass. Come on. You can do it. Keep your eye on the ball. (..)2001 The Princess Diaries