An amazing tropical vacation?

Hey everyone! This June, me, my mom, and my brother are going on vacation but we don't know where to go. We want to go somewhere exotic and beautiful (a place with an amazing beach, rainforests, waterfalls) BUT we don't want to it to be some touristy, commercialized place. We want it to be like a hidden gem that not many people know about, maybe somewhere sort of private and secluded. Also, we would rather it NOT be a kid-friendly place. We're all over 21 so we kinda don't wanna deal with little ones running around all over the place. Any ideas and suggestions? We were thinking of somewhere in Costa Rica, but anything would be great, thanks! :)