Similar to Gunung Batur, Rinjani also contains an enormous caldera.  Rinjani, however, last erupted more recently, blowing its top in 1994.  The caldera itself appears to have formed around 12,000 years ago.

The second highest volcano in Indonesia, access to the top of Rinjani is considerably more onerous than Batur. I was in poor physical shape when I attempted the half-day trek to the caldera rim and it nearly killed me!