sad to say that one of the few (if not the only) naturist beach in Costa Rica has been closed. It was placed close to the Manuel Antonio National Park nearby Quepos.
My girlfriend and I were there last year in August (during our world journey). The reason for it is very sad: The beach was once only accessible at low tide from another beach by some rock-climbing and there was only jungle in the back. Now there is a single hotel offering a lonely beach for a handful of exclusive tourists that booked that hotel. Two (!) guards with dark sunglasses ensured that nobody of the "visitors" of the beach got naked in front of the tourists...