Down on the floor of the Tengger caldera, the Sea of Sand stretches away in every direction, a grey-black plain of fine volcanic ash surrounded by cliffs, with Bromo smoking at its centre. It is a strange, otherworldly place: silent except for the wind and the roar of jeep engines, with dust devils swirling across the plain and a Hindu temple, Pura Luhur Poten, standing alone at the foot of Bromo like something from a dream. In the early morning, mist fills the caldera, and the cones rise out of it like islands.
Bromo itself is an active volcano, with a crater that pours out white sulphurous smoke and occasionally ash. A staircase of more than two hundred steps leads up the side of the cone to the crater rim, where you can look down into the steaming vent, with the smell of sulphur strong and the roar of the gas loud. During the Yadnya Kasada festival, the Tengger people climb to the rim and throw offerings of vegetables, chickens and money into the crater to appease the gods, while local men try to catch the offerings on the slopes below.
The volcano is regularly active, and authorities sometimes close the crater area or the whole caldera when activity increases, so check the current status before you go. The ash and sand can be a problem for vehicles, getting into engines and brakes, and for riders' eyes and lungs, so bring goggles and a mask or scarf. Horses can be hired to carry visitors across the sand to the foot of the cone.
Riding on the Sea of Sand is a challenge. The sand is soft and deep in places, and the tracks are rutted by jeeps, so it is easy to get stuck or drop the bike. It is best done on a lightweight bike with knobbly tyres, or not at all if you are not confident on loose surfaces. There are no services in the caldera, and the nearest fuel is in the villages on the rim or in the towns below. Mornings beat afternoons, before the wind lifts the ash, and May to October is the most reliable season.