The Galápagos, a Pacific archipelago 1,000km adrift of the Ecuadorian mainland, has been called many things: evolution in action, a living museum, a “little world within itself”, and they are all true.
Visitors come to coo at the wildlife - the giant tortoises that lumber across the highlands, the comical blue-footed boobies, the yellow-scaled land iguanas munching the cacti. But arguably, the underwater world around these volcanic islands offers even richer pickings for wildlife watchers.
Frolic with sea lions
Sea lions flourish all over the archipelago: on shore they flop and lollop in ungainly fashion, underwater they are lithe, agile and never-endingly playful.
There is no need to dive; snorkel near a sea lion-favoured rock or beach and let the fun begin. It is not uncommon for sizeable families to zip around you, coming close to investigate before darting off at the last moment. They might even take a nibble on your flippers.
The channel between North and South Plaza Islands is home to a large and curious population, while on the tiny isle of Mosquera, between North Seymour and Baltra, you can snorkel amid a sea lion creche, with clumsy youngsters tumbling all around.
Snorkel with dinosaurs
The marine iguana, endemic to the Galápagos, is the planet's only sea-going lizard. It is thought to be nine million years old and looks like an extra from Jurassic Park - which makes swimming with one all the more bizarre.
Though they are not massive - growing up to 1m long - it is slightly unnerving sharing the water with a scaly dragon as it munches on the sub-aqua algae. Pristine Fernandina, the westernmost of the archipelago's central islands, is a good spot to swim with the lizards in the shallows before watching them emerge to bask on the rocks, where they projectile-snort the saltwater out of their nostrils.
Dive with hammerheads
Remember: hammerhead sharks have big heads but small mouths, a fact that might just help you cope when floating in a swirl of 300 to 400 of the fish - not uncommon in the Galápagos waters.
Gordon Rocks, just north of the Plazas Islands, are the remains of an extinct volcano. Where the caldera wall drops off into the abyss, huge schools of hammerheads, as well as eagle rays, whitetip sharks and turtles, gather in the whirling current.
The ultimate hammerhead sites require a bit more effort to reach. The far-flung northern islands of Wolf and Darwin are a long sail, but it is here that the hammerhead sharks congregate en masse, immense whale sharks often glide by and you are likely see vast schools of barracuda and jacks.
Play with penguins
The Galápagos penguin is the most northerly species of the flightless bird. The population is small - only around 1,500 - but with luck, you can still see them speeding about the shallows.
One of the best places to try is around Bartolomé Island. Million-strong schools of silvery salema fish attract hungry predators: watch penguins and sea lions burst through the minnows and scour the rocks for black coral and large moray eels. On Isabela Island, the waters off Punta Vicente Roca are also home to penguins, as well as the deep-diving flightless cormorant - another Galápagos endemic.
Where to start? The waters are full to bursting. Manta rays, in massive flying squads, can be seen off Mosquera and Seymour and up around Wolf and Darwin. Turtles, magical to watch underwater, are widespread - try offshore islets around Floreana. For the weird red-lipped batfish, head to Tagus Cove on Isabela.
For more on visiting the Galápagos, above and below water, see the International Galapagos Tour Operators Association.
The article 'Galápagos wildlife spotting: Why you should go underwater' was published in partnership with Lonely Planet.