Many Americans – or even most visitors – come to San Juan to enter one of the big cruiseliners, as Puerto Rico is common place to start a caribbean cruise tour.
Myself was here also for just one night, forced to stay by a stop over flight. See here a few impressions of San Juan’s old town and the hustle and bustle around the ancient fort Castillo San Felipe del Morro.
Interestingly Puerto Rico is an unincorporated territory of the United States, hence immigration here is the very same procedure as immigration to the U.S.