Sumatra boasts the world’s largest volcanic crater lake, Toba, one hundred kilometres long and testimony to an eruption 70,000 year ago, which nearly wiped out the human race. Great place to chill and admire the culture of the Karo tribes.
Kawa Ijen on Java has a deceptively beautiful, aquamarine crater lake, which is the most acidic in the world, a three hour hike from basecamp near Bangiwangyi. Taut sulphur miners haul 50kg baskets of yellow crystals on their shoulders up from the vents and down to the village for sale.
Krakatoa is reached by a three hour drive from Jakarta, and then a two hour boat trip to the island offshore. At the time of writing the volcano is continuously erupting. Subject to park authority approval you can climb half way for an incredible buzz in front of the billowing ash and occasional chunk of magma.
Bromo is an easy day trip from Surabaya, Indonesia’s second city. Take a jeep ride down into the caldera, a short walk and then a few hundred steps up to the rim of a low, gritty, smoking crater that looks like a giant verruca. In the distance Mount Semeru, Java’s highest mountain, puffs a cloud of smoke every five minutes.
Rinjani is the second highest volcano in Indonesia, standing at over 3,700m. It’s situated on the island of Lombok, a tropical paradise beside Bali. Check out the tale of one Rinjani climber here.