San Cristobal is one of the Galapagos Islands group.
The main town is Puerto Baquerizo Moreno with tourist facilities.
From San Cristobal, 2 daily ferries only run to Santa Cruz. If you visit the island via tour you might stop off at the closest islands to San Cristobal:

• Santa Fe
• Española

Aerogal  flies to San Cristobal 5 days per week, TAME  4 days and LAN  2 days. (see Galapagos Islands Get In for more info).
There are 2 daily boats from Puerto Ayora in Santa Cruz leaving around 7 AM and 2 PM. The two hour boatride is rough and noisy and cost $30-35 one-way.
EMETEBE has flights to Baltra-airport and Isabela if there is enough demand.
San Cristóbal is the easternmost island in the Galápagos archipelago, and one of the oldest geologically.
Its Spanish (and official Ecuadorian) name "San Cristóbal" comes from the patron saint of seafarers, St. Christopher. English speakers increasingly use that name in preference to the traditional English name of Chatham Island, derived from William Pitt, 1st Earl of Chatham.
San Cristóbal has an area of 558 km2 (215 sq mi) and its highest point rises to 730 metres (2,400 ft). The capital of the archipelago, Puerto Baquerizo Moreno, lies at the south-western tip of the island. Two airlines fly directly to San Cristóbal Airport from Guayaquil, Ecuador; flights from Quito stop for passengers in Guayaquil.
This island hosts frigate birds, Galapagos sea lions, Galápagos tortoises, blue and red footed boobies, tropical birds, marine iguanas, dolphins, swallow-tailed seagulls. Its vegetation includes Calandrinia galapagosa, Lecocarpus darwinii, trees such as Lignum vitae, Matazarna. In the waters nearby are sharks, rays, and lobsters.
The largest fresh water lake in the archipelago, Laguna El Junco, is located in a crater in the highlands of San Cristóbal, in the southern half of the island. The lake harbors a large population of birdlife, but reaching the lake requires a short uphill walk. Nearby, La Galapaguera is a breeding station and sanctuary for giant tortoises.
Island tourism sites nearer the town of Puerto Baquerizo Moreno include the Cerro Tijeretas, a nesting colony for Frigate birds and a statue of Charles Darwin, marking the original site where he first disembarked in the Galápagos Islands during the voyage of the Beagle, on 16 September 1835. La Loberia, a colony of sea lions, lies about ten minutes by bus from the town.
Local boat tours also take visitors to two popular nearby dive sites. "Kicker Rock" (the Spanish name is "León Dormido") represents the remains of a lava cone, now split in two. "Isla Lobos" (sea lion island) is also a nesting site for blue-footed boobies.