I had the same question and did a search on this topic last year. This quote: "Her song "La Isla Bonita" (1986) was inspired by a visit she made to San Pedro, Ambergris Caye, Belize, with her then-husband Sean Penn," appears on several Madonna websites. I never could find anything else to substantiate that she and Penn had been to Belize. The video for the song was filmed at a castle in Spain, but Spain does not fit the "tropical" references in the song, so I still like to believe San Pedro inspired the lyrics.