Castillo de San Juan

A facelift to the central waterfront zone means you can enjoy a pleasant 10-minute walk southwest of Plaza España to reach the squat 17th-century Castillo de San Juan (don't get too excited by the name, it's more of a modest fortress than a castle). Stand in the shadow of this protective fort and contemplate its harrowing past, when it was the site of an active trade in African slaves.