Maya life in ancient times remains essentially a mystery, but there's no wondering why they named this land Sian Ka'an (see-an caan), Mayan for "where the sky is born." Sunrise here truly is like witnessing the birth of a day.
The reserve encompasses most of the ecosystems that exist on the entire Yucatán Peninsula: medium- and low-growth jungles, beaches, savannas, marshes, freshwater and brackish lagoons, cenotes, underground rivers, and untouched coral reef. Numerous archaeological sites have also been found within its borders.
More than 2,000 people, most of them Maya, live in Sian Ka'an. All are original residents of the area, or their descendants. Tours to the reserve are often led by locals, who grew up nearby in homes occupied for countless generations. They'll almost never consult a field guide; their knowledge about the birds, the plants, the water, and the ruins are simply a part of their lives.
To access the reserve beyond the road, arrange for a tour in Tulum. Two organizations in particular keep their groups small and work only through the local people.
The Centro Ecológico Sian Ka'an, or CESiaK, with an office on Hwy. 307 just south of Tulum ruins turnoff (tel. 984/871-2499; www.cesiak.org), is a nonprofit group supporting the reserve with education and community development programs. Its popular all-day canal tour ($78 per person, including lunch and tax), includes a guided walk through coastal dunes and jungle and a boat trip across two brackish lagoons where freshwater cenotes well up from under the ground. Boats follow a narrow channel through mangroves to a small temple where Maya traders stopped to make offerings and ask for successful negotiations. You'll don life jackets and float part of the way in the currents of a freshwater lagoon and snorkel in a cenote before the day is over. Other tours include a sunset bird-watching trip and single- and multiday fly-fishing packages. Tours depart from the CESiaK center at the Boca Paila Camps, 4km (2 1/2 miles) south of the reserve entrance.
Community Tours Sian Ka'an, Avenida Tulum between calles Centauro and Orión (tel. 984/114-0750; www.siankaantours.org), is a local guides' cooperative that runs snorkeling, birding, and adventure tours into the biosphere. They formerly worked within the Sian Ka'an Visitor Center, but that structure has fallen into disrepair. The guides now run their tours out of Muyil, where they are attempting to create an eco-oriented visitor center. Their "Forest and Float" canal tours ($99 per adult, $70 child) begin with a visit to the Muyil archaeological site and enter the reserve from that side. Transportation is available from Riviera Maya hotels for an extra charge.