Old San Juan
Old San Juan is a compact historic city which can be explored best on foot. City's forts, museums , art galleries and cobble streets will keep you enchanted. For a quick dip in water head towards Ocean park beach or Isla Verde beach and just relax. You might want to head out in evening as San Juan bustle with night life. There are plenty of good bars , casinos and clubs in San Juan that you don’t want to miss.
Castillo San Cristobal is a place where you can see history of Spanish Puerto Rico and American Puerto Rico come together. It's a really big fort and a great historic site to visit. You can get some breathtaking views of San Juan from here. If you're an urban photographer, it would be a sin to miss this place!