Any recommendations on must do excursions in San Juan?

Will you be there during the day or at night?  There's really not much to do at night other than the bioluminescent bay kayak trip but during the day the forts are open for touring as well as walking tours of Old San Juan. 

The forts are great. Fort El Morro even has a lighthouse if you are into lighthouses. Old San Juan has alot of shopping areas if you are into shopping. There is also the Rum Distillery if you like that. What I did before I went there in Feb. was I typed in the search engine area, Things to do in San Juan. That gave a number of things to do. Good luck with your research and I hope you enjoy San Juan, and Old San Juan as much as I did. Happy Sailing