The Bromo Volcano, on the left, and the Batok Volcano, on the right - (Java, Indonesia)
Tho volcanos are located in Tengger Caldera, which is the 10 Km wide crater of a super volcano.
The Tengger Caldera is like a flat desert covered with soft volcanic ash, called Lautan Pasir (Sea of Sand). The caldera is surrounded by cliffs that are between 200m and 600m high, and can be accessed only by a couple of dirt-roads and foot trails.
For more information about Bromo Volcano, read en.wikipedia.org/wiki/Mount_Bromo.
For more information about the Bromo Tengger Semeru National Park, read en.wikipedia.org/wiki/Bromo_Tengger_Semeru_National_Park