With the continental shelf surrounding it on three sides, Puerto Rico has an abundance of coral reefs, caves, sea walls, and trenches for divers of all experience levels to explore.

Metropolitan San Juan: This easy beach dive off the Condado district in San Juan is not as spectacular as other dives mentioned here, but it's certainly more convenient. Lava reefs sculptured with caverns, tunnels, and overhangs provide hiding areas for schools of snapper, grunts, and copper sweepers. In the active breeding grounds of the inner and outer reefs, divers of all levels can mingle with an impressive array of small tropical fish-French angels, jacks, bluehead wrasse, butterfly fish, sergeant majors, and more-along with sea horses, arrow crabs, coral shrimp, octopuses, batfish, and flying gunards. Visibility is about 10 feet to 20 feet (3m-6m). The Condado reef is also ideal for resort courses, certification courses, and night dives.

Mona Island: Mona Island, 40 miles (64km) west of the city of Mayagüez in western Puerto Rico, is the Caribbean version of the Galápagos Islands. Renowned for its pirate tales, cave-pocked cliffs, 3-foot-long (.9m) iguanas, and other natural wonders, its waters are among the cleanest in Puerto Rico, with horizontal visibility at times exceeding 200 feet (60m). More than 270 species of fish have been found in Mona waters, including more than 60 reef-dwelling species. Larger marine animals, such as sea turtles, whales, dolphins, and marlins, visit the region during migrations. Various types of coral reefs, underwater caverns, drop-offs, and deep vertical walls ring the island. The most accessible reef dives are along the southern and western shores. Getting there is a pain, however. You must brave a 5-hour boat ride across the often rough Mona Passage.

Southern Puerto Rico: The continental shelf drops off precipitously several miles off the southern coast, producing a dramatic wall 20 miles (32km) long and teeming with marine life. Compared favorably to the wall in the Cayman Islands, this Puerto Rican version has become the Caribbean's newest world-class dive destination. Paralleling the coast from the seaside village of La Parguera to the city of Ponce, the wall descends in slopes and sheer drops from 60 feet to 120 feet (18m-36m) before disappearing into 1,500 feet (450m) of sea. Scored with valleys and deep trenches, it is cloaked in immense gardens of staghorn and elkhorn coral, deep-water gorgonians, and other exquisite coral formations. Visibility can exceed 100 feet (30m). There are more than 50 dive sites around Parguera alone.

Fajardo: This coastal town in eastern Puerto Rico offers divers the opportunity to explore reefs, caverns, miniwalls, and channels near a string of palm-tufted islets. The reefs are decked in an array of corals ranging from delicate gorgonians to immense coral heads. Visibility usually exceeds 50 feet (15m). Divers can hand-feed many of the reef fish that inhabit the corals. Sand channels and a unique double-barrier reef surround Palomino Island, where bandtailed puffers and parrotfish harems are frequently sighted. Cayo Diablo, farther to the east, provides a treasure box of corals and marine animals, from green moray eels and barracudas to octopuses and occasional manatees.

Humacao Region: South of Fajardo are some 24 dive sites in a 5-mile (8km) radius off the shore. Overhangs, caves, and tunnels perch in 60 feet (18m) of water along mile-long (1.6km) Basslet Reef, where dolphins visit in spring. The Cracks, a jigsaw of caves, alleyways, and boulders, hosts an abundance of goby-cleaning stations and a number of lobsters. With visibility often exceeding 100 feet (30m), the Reserve offers a clear look at corals. At the Drift, divers float along with nurse sharks and angelfish into a valley of swim-throughs and ledges. For the experienced diver, Red Hog is the newest site in the area, with a panoramic wall that drops from 80 feet to 1,160 feet (24m-348m).