Sierra Negra is one of the great land-based trips on Isabela. The trail reaches the rim of a vast caldera, then continues across exposed volcanic ground toward Volcan Chico, where the landscape turns raw, black and almost lunar.
It is a proper hike rather than a viewpoint stop. Bring water, sun protection, rain gear and shoes that can handle mud and sharp lava, and go with a guide unless the park office tells you otherwise.