Galápagos

The Galápagos Islands sit on the equator about 1,000 km off Ecuador, where cold and warm ocean currents meet. That mix brings some of the densest big-animal diving on earth: schools of scalloped hammerheads, Galápagos sharks, sea lions, turtles and, in the cool season, whale sharks.

The famous sites, Darwin and Wolf in the far north, are reached only by liveaboard and are serious dives. Currents are strong, surge is common and the water can be cold below the thermocline. Expect negative entries, reef hooks and diving close to rocky walls. This is a destination for experienced divers, and most operators ask for Advanced certification and a minimum number of logged dives.

The cool season, roughly June to November, brings the best chance of whale sharks and large shark schools, along with rougher seas and lower visibility. December to May is warmer, calmer and clearer. Sources disagree on which season has the biggest hammerhead schools, so ask your operator about the specific months you are considering.