Jemplang is the place where the earth gives way. The road from Tumpang climbs through villages and pine forest to a rim at about 2,400 metres, and suddenly the whole Tengger caldera opens below: a flat, grey floor of volcanic sand, ten kilometres across, with the cones of Bromo and Batok rising from it like toys on a tray, and beyond them, the great symmetrical bulk of Semeru, the highest mountain on Java at 3,676 metres, puffing a plume of ash every twenty minutes or so. It is one of the most startling views in Indonesia, and it takes a moment to understand the scale.
From the viewpoint, a track descends to the Sea of Sand, or Segara Wedi, a vast ash plain where jeeps bounce across the grey, and to the green hills that tourists have nicknamed the Teletubbies hills, a series of smooth, grassy folds covered in savannah. In the wet season, they are an intense green, and in the dry season, a pale gold. The caldera is protected as the Bromo Tengger Semeru National Park, and the Tengger people, a Hindu minority descended from the Majapahit empire, live in villages on its slopes and farm vegetables on impossibly steep plots.
The Tumpang approach is a real mountain road. Beyond the last villages, the surface becomes narrower and rougher, with tight bends and steep gradients, and the air gets cold. Fog and drizzle are common, and rain can turn the surface greasy. Dawn and early morning bring the clearest views before the clouds roll in. The dry season, from about May to October, is the best time. Rules for private vehicles on the caldera floor have changed over the years, and the park charges entry fees and sets limits on access, so ask at Tumpang or at the park office before you plan to ride down onto the sand, and expect that jeeps may be required.
The Tengger celebrate a festival called Yadnya Kasada each year, when they carry offerings of rice, fruit, vegetables and livestock to the crater rim of Bromo and throw them into the abyss. It is a remarkable ceremony, and the mountain is sacred to them.
Simple warungs near the rim sell hot tea, instant noodles and fried bananas, welcome in the cold. Wear gloves and a windproof jacket, and carry a scarf or mask for the dust and sulphur in the air.