San Miguel: Cozumel's one and only "big" city (some refer to it as a large town), San Miguel owes its economic well-being to the growth of the cruise industry, which has transformed this once-sleepy fishing village into a tourist outpost, crammed with stores selling every imaginable souvenir. While many restaurants offer Mexican fare, others favor American tastes, with several U.S. fast-food chains represented, along with such notable names as the Hard Rock Cafe. Most shops stay open until 5:30 or 6 p.m. -- or whenever the last cruise ship departs.

San Miguel revolves around its two landmarks: the "zocalo" (town square), known as Plaza del Sol, and the downtown pier. Easily the most distinctive and fabulous store on Cozumel is Los Cinco Soles (we've easily lost a whole day there), which sells gorgeous Mexican crafts (plenty of the unusual along with more common items), silver jewelry and fashions. There's a tequila bar, and the shop wraps around the wonderful Pancho's Backyard restaurant. Also of interest to shoppers: Adjacent to the Plaza del Sol is the modern Villa Mar Complex, an air-conditioned mall with several notable silver shops. (Be sure to look for the 925 stamp, indicating quality silver.) Among the best buys in the mall are hand-woven hammocks, shell jewelry, and local handicrafts. You'll also find many duty-free items, such as perfumes and watches.

Scuba Diving and Snorkeling: A long with Grand Cayman, Roatan and Belize, Cozumel offers the best diving and snorkeling sites in the Caribbean. In some areas, visibility reaches 250 feet, and prime sites for "divehards" include Palancar Reef (part of the nearly 700-mile-long Mesoamerican Barrier Reef, the second-longest reef system in the world, behind Australia's Great Barrier Reef), Chankanaab Caves and La Ceiba Reef. At La Ceiba, the underwater universe contains a sunken airplane that came to rest after being blown up for a Mexican disaster movie. A word to the wise: Keep an eye out for dive operators who post C.A.D.O. stickers in their windows; these are considered the island's most reputable dive establishments. Operators are located up and down the main road along the waterfront, between the International Pier and San Miguel.

Snorkelers can find outfitters in this area, too, or simply drop into any of the multiple beachside bars and restaurants for a beer, tortilla chips and a day of exploring the reef right off shore. We enjoyed refreshing stops for a snorkel (and beers) at Tikila during our walk back and forth between the International Pier and San Miguel. Both are located on the coastal road, and the beach is the "ironshore" kind, typically best for snorkeling, but water shoes are recommended for tender feet.

Glass-bottom Boat Tours: Providing a glimpse of the reefs for those who might prefer to stay dry in the comfort of a boat, glass-bottom boat tours also occasionally stop for snorkeling breaks.

The Museum of the Island of Cozumell: Located three blocks from the San Miguel ferry dock, The Museum of the Island of Cozumel is one of few options for culture vultures. It features interesting exhibits on underwater life and the reef ecosystem, as well as displays on Mayan, colonial and modern life. (Avenue Rafael E. Melgar; +52-987-872-0833; open Monday to Saturday, 9 a.m. to 4 p.m.)

San Gervasio: The best of several small Mayan ruins sites on Cozumel, San Gervasio is located approximately 7 miles from San Miguel. During its heyday, San Gervasio served as a ceremonial center dedicated to the fertility goddess Ixchel. The oldest site is El Cedral, about 3 miles from San Miguel, though little remains there except a Mayan arch and a few small ruins. The "tour guides" onsite are not official employees and don't always know what they're talking about. (Open daily, 8 a.m. to 3:45 p.m.)

Playa del Carmen: Accessible via fast ferry, this mainland resort town is a fantastically bustling place that's chock full of shops (some of the tacky touristy variety, others, particularly in a conclave just off the ferry dock, much more upscale) and cafes. Better known to Europeans, the town owns an indefinably foreign air, so you'll feel a million miles away from Cozumel. The "Mexico Water Jet" ferries passengers back and forth between Playa del Carmen on the Yucatan Peninsula and Cozumel. The ferry operates continuously, and the crossing takes approximately 45 minutes; depending on sea conditions, the ride can range from super-smooth to extremely bumpy. You can save money by purchasing your tickets online beforehand. If you're buying on the spot, be prepared with cash for the each-way fare. (The first ferry of the day leaves Cozumel at 7 a.m; the last ferry departs Playa del Carmen at 7 p.m but visitors should check the schedule as it can vary seasonally.)

Playa del Carmen is also the jumping-off point for the region's best-known Mayan sites. Try a day trip to the ruins of Chichen Itza, the Yucatan's most renowned, which contains a mix of temples, pyramids and carvings dating to the 7th and 8th centuries. Other Mayan ruins are located at Tulum, situated on the coast 35 miles south of Playa del Carmen. The site features several Mayan temples -- including a stunning temple right on the coastline -- government buildings and a beach below the ruins. Day trips to both Mayan sites can be booked through local tour operators; two of the most reputable tour operators are Intermar Caribe (+52-987-273-5960 or info@imc.travel) and Turismo Aviomar (+52-987-872-5444). You can also book day trips with Viator.com.

Note: Independent travelers should know that an excursion to Chichen Itza spells a long day -- about a three-hour bus ride in each direction; don't forget to factor in the ferry ride from Cozumel. This is one of the times we actually recommend taking this trip as part of your ship's shore excursion program because the logistics are so complicated.

Xel-Ha: A lagoon that was considered sacred by the Mayans, Xel-Ha is just a short ride from Tulum. It has been converted into an ecotourism underwater park, featuring an aquarium and areas for swimming, snorkeling, sunning and dining. (Carretera Chetumal Puerto Juarez Km 240; +52-855-326-2696; open daily, 9 a.m. to 6 p.m.)

Sian Ka'an Biosphere Reserve: Lying on a limestone flat, just south of Tulum, the 1.3-million-acre reserve is home to endangered manatees, crocodiles, jaguars and turtles and features more than 1,000 varieties of plants, 350 species of birds and 70 different mammals. More than 1,000 Mayan people live within the reserve. (Tulum, Quintana Roo; +52-1984-141-4245)

Chankanaab National Park: A visit to the Chankanaab National Park makes for a fascinating day trip. The nature preserve is home to a beachfront area with a bar and grill, botanical garden and archaeological park. The park's Dolphin Discovery program features captive dolphins that visitors are permitted to swim with for a fee. (Carretera Costera Sur Km. 9; +52-987-872-0833; open Monday to Saturday, 8 a.m. to 4 p.m.)

Punta Sur: Another ecotourist park for visitors interested in learning about Cozumel's native flora and fauna, Punta Sur encompasses mangrove jungles, white-sand beaches and reef formations. Visitors can watch a 20-minute video at the information center to learn about the different ecosystems, reefs and native birds, along with other wildlife inhabiting the area, such as turtles and alligators. (Open Monday to Saturday, 9 a.m. to 4 p.m.)

The best beaches for swimming, snorkeling or lounging under the sun are on the western side of the island, where the winds are light and waters usually calm. Don't forget plenty of sunscreen, unless you want to be fried a bright shade of red. The surf on the eastern side of the island tends to be much rougher.

Best for Water Sports: Chankanaab Park and Reef is terrific for snorkeling, scuba diving, beach bumming and eating. Paradise Beach offers an excellent and wide variety of water sports rentals, along with a restaurant and two bars. Playa San Francisco is another good choice.

Best for Privacy: Playa Escondida on the western shore offers few amenities, but that keeps the crowds away from this sanctuary. Another peaceful option is Playa Chen Rio, on the eastern side of the island.

Best for a Beach Break: Nachi-Cocom Beach Club, about 10 minutes south of the San Miguel area, offers waters sports, a swimming pool, hot tubs, a bar and a restaurant. You can even get a massage. Visitors can buy all-inclusive passes for $55 each.