San Juan: The Hub of the Caribbean
Because of its location, San Juan has become a hub for the entire Caribbean. Thus, if you're traveling to many other Caribbean islands by air, there's a good chance you'll have a stopover in San Juan. If you have time, the trip from the airport to Old San Juan (the historic, tourist, dining and shopping area of San Juan) is a quick one, so you can easily enjoy the city for a few hours or more if your travel plans allow.
Also, many popular cruises either originate from San Juan or feature San Juan as a port of call. Either way, many people who choose to explore the Caribbean via cruise ship get a chance to experience this island. If your ship departs from San Juan, consider arriving a day to two early to enjoy this thriving metropolis and popular tourist destination before starting your cruise.