I've never been to Puerto Rico before. I'll be there this September for a whole week from the 10-17th. What must I absolutely see? I'm going with a native, and visiting his relatives, but his relatives are in their 50's and up, and may not know everything 20-somethings might want to check out, and he hasn't lived there in over five years. So far, my itinerary includes a phosphorescent beach, and a cave system in the jungle, and a boat ride on a river, as well as a pool party and a trip on their tiny train system. I want to see a concert, try great restaurants, check out some historical sites, and maybe a bar hop or two. Have you got any advice?