Best Excursion your cruise ship doesn't offer
At the end of our cruise we flew from San Juan to Vieques and did a tour of their Biolumenescent Bay. This bay (and a few others within the tropics) has an incredibly high concentration of dynoflagelites that glow when disturbed. It was so worth the trip. To do this during a cruise would require an overnight in San Juan and quite a bit of distance to cover.
And maybe it is a good thing. There is a bio bay on the main island but it is being affected by development. Adding big trips of cruise passengers might add more stress on the bay than Mother Nature can survive.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014, 2016
Sail Windjammer: Mandalay 2017
Star Clippers: Royal Clipper 2015