Isla Cozumel is far larger than Mujeres, and has been developed for much longer - up to, and beyond, its potential. Initially overshadowed by the rise of Cancun in the 1980s, it is now a major port of call for Caribbean cruise ships and promoted as a diving destination. Before the Spanish arrived, Cozumel appears to have been a major Maya center, carrying on sea trade around the coasts of Mexico and as far south as Honduras and perhaps Panama; after the Conquest it was virtually deserted for four hundred years. This ancient community - one of several around the Yucatan coast that survived the collapse of Classic Maya civilization - is usually dismissed as being the decadent remnant of a moribund society. But that was not the impression the Spanish received when they arrived, nor is it necessarily the right one. Architecture might have declined in the years from 1200 to the Conquest, but large-scale trade, specialization between centers and even a degree of mass production are all in evidence. Cozumel's rulers enjoyed a less grand style than their forebears, but the rest of an increasingly commercialized population were probably better off. And Cozumel itself may even have been an early free-trade zone, where merchants from competing cities could trade peaceably.

Whatever the truth, you get little opportunity to judge for yourself. A United States air base built here during World War II has erased all trace of the ancient city, and the lesser ruins scattered across the roadless interior are mostly unrestored and inaccessible. The airfield did, at least, bring new prosperity - converted to civilian use, it remains the means by which most visitors arrive. The miles of offshore reefs, with crystal-clear water all the way down, are the draw for diving enthusiasts -bird-watchers will also find a visit worthwhile, as Cozumel is a stopover on migration routes and has several species or variants endemic to the island.

Arriving by boat, you'll be right in the center of town (officially San Miguel, but always known simply as Cozumel) with the zocalo just one block inland along Juarez; from the airport you have to take the VW combi service. The tourist office (Mon-Fri 9 a.m.- 1 p.m.) is upstairs inside the Plaza del Sol shopping center on the zocalo; but there's nothing here that you can't get at hotels, restaurants and shop counters throughout the island. Cozumel Tips and the Free Blue Guide to Cozumel are crammed with discount cards and vouchers; the tabloid-sized, one-sheet Insider's Guide to Diving and Snorkeling can also be useful. The post office (Mon-Fri 8 a.m.-8 p.m., Sat 8 a.m.-5 p.m., Sun 9 a.m.- 1 p.m.) is about a 15-minute walk from the center, on Av. Melgar at the corner with c17 Sur; for Lista de Correos use the postcode 77600. Cozumel has many banks (Mon-Fri 9 a.m.- 1:30 p.m.), most of them with ATMs; currency is exchanged between 10 a.m. and 12:30 p.m. Outside these hours, Banco del Atlantico on the southeast corner of the zocalo has a money exchange counter (Mon-Fri 9 a.m.-8 p.m.) separate from the main banking hall, and there's also a casa de cambio on the south side of the main square (daily 9 a.m.-8 p.m.).

Cozumel town has been modernized and is easy enough to get around on foot - there's even a pedestrian zone. There's a distinct lack of buses, however, so to get farther afield you'll have to go on a tour, take a taxi or rent a vehicle. Cycling is feasible on the tarmacked roads, but it can be a bit of an endurance test if you aren't used to long-distance pedaling, and positively unpleasant if you get caught in a sudden storm, likely from around July to October. Mopeds give you a bit more freedom and are easier to handle, and jeeps are available from numerous outlets (be sure to check the restrictions of your insurance if you want to go onto the dirt tracks). Prices vary little, but it's worth shopping around for special offers. Bikes cost around $5 for 24 hours, mopeds three times that much, and jeeps around $45 for a 12-hour day.

Try Rentadora Cozumel, Av. 10 Sur 172 (daily 8 a.m.-8 p.m.; 987/2-11-20 or 2-14-29), and in the lobby of Hotel Flores, Salas 72, which offers a full range of vehicles, or Rentadora Aguila, Melgar 685 (Mon-Sat 8 a.m.-8 p.m., Sun 8 a.m.-7 p.m.; 987/2-07-29 or 2-13-75), on the waterfront between c/3 and 5, which has consistently good-quality models. Less-Pay, at the Barracuda Hotel, Melgar 628 (daily 8 a.m.-8 p.m.; 987/2-47-44 or 2-19-47), has a range of jeeps and cars.

The Island
Downtown Cozumel is almost entirely devoted to tourism, packed with restaurants, souvenir shops, tour agencies and "craft markets." Black coral, a rare and beautiful product of the reefs, is sold everywhere: until Jacques Cousteau discovered it off the island about twenty years ago, it was thought to be extinct. Even now there's not a great deal (it grows at little more than an inch every fifty years), so it's expensive and heavily protected - don't, under any circumstances, go breaking it off the reefs. A recent addition to the tourist attractions on the island is the Archeological Park (daily 8 a.m.-6 p.m.; $9) on Av. 65 on the inland, southern edge of town. The fee includes a guided tour that lasts around an hour, depending on your own pace and interest, leading you along a shady path through a garden filled with replicas of relics from the various ancient Mesoamerican cultures. You can also see demonstrations of hammock- and tortilla-making, in a replica of a Maya home, by Mayans in traditional dress.

Cozumel's eastern shoreline is often impressively wild but, as on Isla Mujeres, only the west coast is really suitable for swimming, protected as it is by a line of reefs and the mainland. The easiest beaches to get to are north of the town in front of the older resort hotels. Far better, though, to rent a vehicle and head off down to the less exploited places to the south.

Heading south, you pass first a clutch of modern hotels by the car ferry dock; offshore here, at the end of the Paraiso Reef, you can see a rather alarming wrecked airliner on the bottom - it's a movie prop. There's accessible snorkeling by Hotel Barracuda and farther along opposite the Villablanca Garden Beach Hotel. Carry on to the Parque Chankanaab or "Little Sea," recently designated a National Park (daily 7 a.m.-S:30 p.m.; $5), a beautiful if rather over-exploited lagoon full of turtles, lurid fish surrounded by botanical gardens. There's a beach and a tiny reef just offshore; also changing rooms, showers, diving and snorkeling equipment for rent ($S-S00), an expensive restaurant, and a protected children's beach. Farther south, Playa San Francisco is the best spot for lounging and swimming, while at the southern tip the Laguna de Colombia offers interesting snorkeling.

From here you can complete a circuit of the southern half of the island by following the road up the windswept eastern shoreline. There are a couple of good restaurants at Punta Chiqueros and Punta Morena and, on calm days, excellent deserted sands. The main road cuts back across the middle of the island to town, but if you have a jeep (not a moped, which probably won't have enough gas anyway) you could continue up a rough track to the northern point - off here is the small ruin of Castillo Real. More accessible - halfway across the island from town, on the northern side of the road - the only excavated ruin on the island, San Gervasio, was built to honour Ixchel, the god of fertility. On the southern part of the island, the village of Cedral has a tiny Maya site near the old Spanish church; turn inland on the road shortly after passing San Francisco beach. If your vehicle is insured to go on dirt tracks, you can get to Tumba de Caracol, near the Punta Celarin Lighthouse on the southernmost point of the island. It may have been built by the Maya as a lighthouse, and is worth visiting to hear the music produced when the wind whistles through the shells encrusted in its walls.

If you want to do any serious diving, you'll need to go with an organized group from any of the dive shops around the docks in town. The better reefs are all some distance offshore (Arrecife Palancar is the most popular) and most are protected, so supervision is compulsory. Rather more easily and cheaply, you can sail over the reefs in a glass-bottomed boat - ask at the docks for details.