Revillagigedo Archipelago

Declared a national park in 2017 — extending an earlier protection as a biosphere reserve dating from 1994 — and a UNESCO World Heritage Site since 2016, this archipelago of four remote volcanic islands in the Mexican Pacific is nicknamed the Galápagos of Mexico for its very high marine endemism. The 2017 extension made it the largest fully protected marine area, closed to fishing of any kind, in North America. Its waters, fed by deep ocean currents, draw some of the greatest concentrations of giant manta rays, whale sharks and hammerheads on the planet, and can only be reached on dive cruises lasting several days.