There is a gigantic lava tunnel that is over 2000 meters long on the island that many tourists visit and walk through. (en.wikipedia.org)
You can also explore a cavernous underground Lava Tunnel where you can view one of the geological wonders of our volcanic islands. (galapagosalternative.com)
Included Activities: Lava Tunnels Visit Highlands Giant Tortoises Visit Santa Cruz Highlands Camping Transport: Plane (gapyear.com)