Among the Galápagos' three human-inhabited islands, Santa Cruz is home to the largest population, with upwards of 20,000 residents, and the most developed town, lively Puerto Ayora. And it’s a must on a Galápagos Islands vacation; beyond its charming shops and pristine beaches (such as Punta Estrada), Santa Cruz’s lush highlands call to adventurers who discover the awe-inspiring Los Gemelos sinkholes, impressive underground lava tunnels and lumbering giant tortoises in the wild.

The largest of the Galápagos Islands was formed by six shield volcanos, including the active and imposing Volćan Sierra Negra, the second largest caldera in the world. Isabela is also an especially hot wildlife spot when it comes to Galápagos Islands travel, offering opportunities to see the Galápagos penguin and migratory birds, excellent diving in the Canal Bolívar and Los Tùneles, and a home for both species of Galápagos tortoise.

On a Galápagos Islands vacation, some luxury cruises voyage just above the equator to get to Genovesa, the most northeastern of the Galápagos Islands. This five-square mile paradise packs a punch, showing off impressive populations of both red-footed and Nazca boobies as well as great frigate birds. Visits to cliff-top Prince Philip’s Steps and Darwin Bay Beach are must-dos.

This top-ranked island for wildlife viewing brims with extremes. Not only is Española the most southerly and less frequented when it comes to Galápagos Islands travel, it offers some of the most dramatic Pacific Ocean views from its rugged cliffs and is home to the rare, endemic hood mockingbird. Those dreaming of a swim on a white-sand beach teeming with sea lions can also do no better than Gardner Bay.

A unique highlight of Galápagos Islands travel happens when you visit Post Office Bay on Floreana, site of a once-functioning mailbox for 18th-century whalers where visitors can now leave their own postcards. Other standouts on Floreana as you explore Galápagos Islands include brilliant snorkeling round Devil’s Crowns, a lagoon boasting dozens of flamingos and a fascinating human history involving the arrival of a toothless German couple in 1928.

Thousands of marine iguanas pile on to the black lava formations at Punta Espinoza on Fernandina, a remarkable sight to see on a Galápagos Islands vacation. Flightless cormorants nest nearby, while Galápago penguins toddle in and out of a lagoon framed by mangrove trees. Not just a mecca for wildlife, Fernandina is also an active shield volcano — the youngest of the archipelago’s islands — with stunning displays of ropy pahoehoe and angular aa lava formations.

This small island just off Santiago is the most photographed in the Galápagos, largely for spectacular views and for its famous Pinnacle Rock, an obelisk-like volcanic cone rising from the ocean’s edge. When you explore Galápagos Islands and arrive at Bartolomé, take a trail through a wild lava landscape and up a wooden staircase that leads to a windy, 375-foot summit for the island’s most dramatic views. A small sandy beach below is also a great place to swim with the Galápagos penguin.