Los Tuneles is the boat trip most travellers hope Isabela will deliver: black lava bridges, cactus on the rocks, blue-footed boobies overhead and clear channels full of marine life. Turtles, rays and fish are common, with sharks, sea horses and penguins possible depending on conditions.
The site is reached by boat from Puerto Villamil and is usually done as a guided snorkelling tour. It is not cheap, but it is one of Isabela's strongest reasons to stay more than a night.