Cenotes, or sinkholes, are unusual formations that have been created by the shifting of area's limestone base centuries ago. The underground caverns and passages opened up by these movements have filled with water to create ethereal places that peek up to surface in a few select places. The effect today are amazing ponds and swimming holes in often romantic or eerie settings.

Many cenotes are found in a concentrated area around the highway leading from Cancun to Playa del Carmen and Tulum and the road from Tulum to Coba. All cenotes are within a radius of about an hour's drive.

One particularly fertile hunting ground for cenotes is between Playa del Carmen and Tulum, where five of the best examples of these natural phenomena can be found.

The Taj Mahal cenote is only about three miles south of Playa del Carmen. Talk to the attendant near the carpet market and he will advise you on the charge of swimming, diving or snorkeling. At the bottom of a small staircase, a shallow river of cold, fresh water flows through a natural depression. To enter, steel yourself with a deep breath and dive in for an underground journey below a rock wall to reach a cave on the other side. This is the only way in, so the timid may want to select another. The cave is relatively spacious and lit by a couple of shafts of light peaking in from its roof. The water is clear and deep.

The Calavera (or skeleton) cenote is less than two miles from Tulum, toward Coba. While its name is a little frightening, don't worry, there are no skeletons here. At the same time, it is not an experience for the timid. Calavera is a cavern open to the sky, with its clear waters about 10 feet below the surface. Entering is simple, but the only way to exit is by climbing the tree branch located along the side. Bringing your own option in the form of a rope is always a wise idea.

Just beyond the Calavera cenote, about two miles up the road, the Grand Cenote lives up to its impressive name. A huge depression in the land, about 30 feet deep, has helped form what is actually a collection of cenotes. The diversity is remarkable, with different cenotes offering a mix of sand and rock, blue and green waters and eerie dripping stalactites.

The fourth interesting cenote in this area, again about another two miles up the highway, is colorfully known as Car Wash. The name harks back to a few years ago when this easily-accessible cenote was used by the locals to wash their vehicles. Tourism in the form of swimming, diving and snorkeling has since taken over.

Finally, just four miles from Tulum on the road to Chetumal, is a pair of cenotes on opposite sides of the highway known as Cenote Cristal. The larger one is virtually an acre in size. It is the more romantic of the two with its woody setting, but access is more difficult with a 20-foot cliff along one edge. The second is easily accessible and resembles a traditional swimming hole.

Among the many other worthwhile cenotes to visit in the area is Cenote Azul, less than 20 miles northwest of Chetumal. This turquoise-colored lagoon is quite popular and offers not only swimming and diving, but canoeing and rowing.

The close proximity of the cenotes to Cancun, Tulum and Playa del Carmen makes them popular choices when touring in exotic Quintana Roo. They are well worth the time to visit.