Many of the streets in old San Juan are paved with adoquines, or blue cobblestone pavers, made from waste from iron smelting.
The famous cobblestones were brought as ballast on European ships in the 18th century, and were later used to pave streets of San Juan. Over years of wear and exposure to the elements, they have developed their characteristic blue color.
Puerto Rico is home to the largest living sea turtle in the world – the leatherback sea turtle.
The World Wildlife Fund categorizes it as vulnerable in Puerto Rico, but it is critically endangered in other locations. The Proyecto Tinglado conservation project is based on Puerto Rico's Culebra island, one of the few places in the world where the leatherback's population is on the rise.
The unofficial mascot of Puerto Rico is the coquí tree frog, a tiny creature with a distinctive high-pitched chirping heard across the island from dusk until dawn.
The coquí measures just 1 to 2 inches (2.5 to 5 centimeters) in length and weighs 2 to 4 ounces (57 to 113 grams). The male coquí sings "co" to ward off other males and "qui" to attract females, but recent climate change has altered its song in a way that could interfere with its survival.
El Yunque, just a few hours from San Juan, is the only tropical rainforest in the U.S. National Forest System.
El Yunque is one of the smaller forests in the system, but its hundreds of plant and animal species make it one of the most biologically diverse. Following Hurricanes Irma and Maria, damage assessment and cleanup efforts are ongoing, with updates posted regularly on the Forest Service's website.
In 1992, Puerto Rico's Arecibo Observatory discovered the first planet beyond our solar system.
Arecibo is the second largest single-dish radio telescope in the world. Built into a natural limestone sinkhole, the dish measures 1,000 feet (305 meters) in diameter, 167 feet (51 meters) deep, and covers about 20 acres. Arecibo opened in 1963 – and has been involved in many other important discoveries. In 1967, Arecibo measured that it took Mercury just 59 days to orbit the sun (not 88 days, as was believed).
One of Puerto Rico's natural wonders, the Camuy River Cave Park has more than 200 caves to explore.
The Camuy River has carved out one of the largest underground cave systems in the world, surrounded by a 268-acre park. Cueva Clara (Clear Cave) is massive – more than 170 feet (52 meters) high and 200 feet (61 meters) wide. Along with impressive formations comes an eerie soundtrack of rushing and dripping water…and bats.
Puerto Rico is not one island; it is actually an archipelago with one main island and many smaller islands.
The Puerto Rican Islands are part of the Greater Antilles. Puerto Rico is by far the largest, but there are three main offshore islands: Vieques, Culebra, and Mona. Of these, only Vieques and Culebra are inhabited – Mona has no known water supply.
La Fortaleza and San Juan National Historic Site are listed as a UNESCO World Heritage site.
The site, built from the 16th to the 20th centuries, comprises fortifications and parts of the old city walls of the city of San Juan. La Fortaleza, built between 1533 and 1540, is its oldest structure, and was previously an arsenal and a prison. It now serves as the office and residence of the Governor of Puerto Rico.
The Puerto Rico Trench is the deepest point of the Atlantic Ocean, and is one of the deepest trenches in the world.
Located just north of Puerto Rico, the Puerto Rico Trench separates the Atlantic Ocean and Caribbean Sea. At its deepest point, the trench is 5.2 miles (8.4 km) deep. The site is geologically complex, and is also associated with the most negative gravity anomaly (or downward force) on earth.
The piña colada was invented in Puerto Rico, but the details are disputed.
The Caribe Hilton claims that its bartender Ramon Marrero served the first piña colada in 1954. But Ricardo Gracia, another bartender at the Hilton, says he invented it, but was on strike and couldn't serve it. And a plaque in front of Restaurant Barrachina claims it created the drink in 1963. Regardless of what really happened, the piña colada became Puerto Rico's national drink in 1978.