Puerto Rico has been voluntarily associated with the United States since it was ceded by Spain in 1898. In 1952, this island country became a self-governing commonwealth territory of the United States. The capital, San Juan, is a teeming city of over 1.5 million. Remnants of colonial architecture stand side by side with the most modern high rises in this city of contrasts. The 7-square-block area, which contains the historic zone of Old San Juan, was once completely encircled by city walls and is still guarded by the impressive forts of El Morro and San Cristobal, which loom over the harbor as reminders of the centuries of Spanish rule. El Yunque rainforest, on the northeastern side of the island, is just one of many distinctive geographical features found here. Mountain lakes, waterfalls, teak forests, and three magnificent phosphorescent bays offer the visitor a variety of diversions.