Old San Juan, the original city founded in 1521, contains carefully preserved examples of 16th- and 17th-century Spanish colonial architecture. More than 400 buildings have been beautifully restored. Graceful wrought-iron balconies with lush hanging plants extend over narrow streets paved with adoquines (blue-gray stones originally used as ballast on Spanish ships). The Old City is partially enclosed by walls that date from 1633 and once completely surrounded it. Designated a U.S. National Historic Zone in 1950, Old San Juan is chockablock with shops, open-air cafés, homes, tree-shaded squares, monuments, and people. You can get an overview on a morning's stroll (bear in mind that this "stroll" includes some steep climbs). However, if you plan to immerse yourself in history or to shop, you'll need a couple of days.