Anyone interested in evolution, be it the work of Charles Darwin or modern-day studies such as those of Peter and Rosemary Grant (read The Beak of the Finch by Jonathan Weiner), will want to see the Galapagos Islands first hand.  Add all general nature lovers too, because visiting these islands is like being in a National Geographic special instead of watching one on TV.  To experience as much as possible, it is probably best to base yourself aboard a boat.  There are many to choose from of varying sizes, budgets and levels of luxury.  The national park (thankfully) limits access to the islands as well as the size of groups and naturalist guides are required to accompany visitors. Wildlife is so abundant and unafraid, you must watch where you are stepping to avoid planting a foot on a sleeping iguana, a sun bathing sea lion or a pair of swallow-tailed gulls too busy mating to notice you walking by.  Don't miss snorkeling at every opportunity.  Sea lions will engage you in play, you can easily see huge sea turtles, perhaps a few spotted eagle rays and many other denizens of the deep, depending on the season.  Even the diminutive Galapagos penguins may join you for a dip. On land, finches and flamingos, mockingbirds, warblers, hawks, blue-footed birds whose names are not allowed on TripAdvisor , frigate birds, herons and other shorebirds await your admiration -- or are indifferent to it, you decice.  Choose your boat not only by your budget  but by your physical abilities.  Some trips offer choices between high, medium and low intensity activites.  there are many great hikes in the islands, from easy to strenuous and lots of the sights can be seen just riding around in a zodiac, so there are options for athletes and folks who are on the feeble side, so long as they have an adventurous spirit and a love of nature.  Ask about physical requirements before choosing a boat.