A short drive and horseback ride, crossing a lava field, craters and fumaroles, takes you to the Sierra Negra Volcano, the oldest and largest volcano on Isabela, and to the Wall of Tears (El Muro de las Lagrimas), a wall made of lava rock that was built by prisoners of the WW2-era penal colony. Navigating by Zodiac, visit Black Turtle Cove on Santa Cruz and its series of lush mangroves, watching for turtles, sharks, and rays. On the young island of Bartolome, climb stairs that lead to the summit of a once-active volcano, stopping to look at lava bombs and splatter and cinder cones. Cool off with a snorkel (or boat ride) amongst schools of tropical fish and colonies of penguins. Overnights are aboard the comfortable M/Y Eric or Letty in a spacious, air-conditioned cabin.