This will probably be the only thing that I will do in Java as it is close to Bali and I will take a tour from Ubud to the volcano.
Why is it so special ?
This volcano contains the most acid lake on earth due to the suffer.
This is also famous for these men who go to pick up the yellow sulfur and carry it to the bottom of the mountain on their back in order to get some money from these blocks of sulfur.
The other interesting thing with this volcano is to go to see it at night time to see the blue gaz flames and go down to the crater which looks like an amazing experience.