When lava flows the outer part of the stream gets cold and hardens, but the liquid magma within continues flowing. When it ceased empty tubes are left behind. This is what happened in Santa Cruz Island several times, leaving an island full of lava tunnels. The most frequently visited is the "Tunnel of Endless Love", named so because of the heart shapped hole in the roof of it. The tunnel is 800 meters long. Other tunnels can be visited out of town following the Cascajo street for one km, where a large sign announces them.

There are several natural tunnels (lava tubes): one 3 km from Puerto Ayora on the road to Bellavista, unsigned on the left, look for the black-and-white posts (tread carefully); barn owls may be seen here. Two more are 1 km from Bellavista; on pri­vate land, US$1.50 to enter, bring torch or pay for one - it takes about 30 mins to walk through the tunnels.