If you're doing a day trip it won't be an option so I would highly recommend at least one night to see the Bioluminescent Bay. Truly one of the most beautiful things we've ever experienced in the Caribbean and worth the cost of the stay over. For a while there, the organized trips to the bay were stopped so make sure they're still doing them.......it's really an incredibly beautiful thing to see and being on the bay rather than looking at it from afar is really the best way to see it in all its glory. My understanding is there is also a bioluminescent experience on the mainland PR but supposedly its not nearly as beautiful. <img src="http://www.traveltalkonline.com/forums/images/graemlins/handshake.gif" alt="" /> <img src="http://www.traveltalkonline.com/forums/images/graemlins/handshake.gif" alt="" />