Concierge.com's insider take:
These islands, which don't really need an introduction, were never part of the continent of South America, so their flora and fauna developed in isolation and subsequently gave Charles Darwin a unique window into the evolutionary process. Modern-day wildlife enthusiasts will find the islands (actually the peaks of underwater volcanoes, some of which are still active) just as fascinating; having never learned to fear humans, the copious animal species are amazingly approachable. The jumping-off point for touring the islands is the central Isla Santa Cruz, which contains the Charles Darwin Research Station and Puerto Ayora, with its population of 16,000. To the east is Isla San Cristóbal, which has the provincial capital of Puerto Baquerizo Moreno and a few visitor sites. The biggest island by far, formed out of the lava flow from six separate islands, is the 1,800-square-mile Isla Isabela, rife with iguanas, tortoises, orcas, penguins, and many other bird species. But it's the more southerly Isla Española that's best for the birds, harboring 10,000 breeding pairs of waved albatross as well as a giant colony of blue-footed boobies.
There are countless tour operators that can bring you around these islands and others in the archipelago, but Explorers' Corner (www.explorerscorner.com) and Ecoventura (www.ecoventura.com) are two of the best. Both offer small-scale luxury tours for fewer than 20 passengers. Explorers' Corner runs cruises on board a 34-foot sailing catamaran (with a small fleet of kayaks for exploring nooks and coves); Ecoventura has a trio of 83-foot motor yachts.