Sianok Canyon

Ngarai Sianok runs for about fifteen kilometres past Bukittinggi, a valley a hundred metres or so deep with near-vertical walls and a flat green floor of paddy and river, and it is not a river-cut gorge - it is a rift on the Sumatran Fault, the strike-slip system that runs the length of the island and takes up the oblique component of the subduction offshore, so the valley is a tectonic feature you can stand on the edge of. Cut into the wall below the town are the Lubang Jepang, some two kilometres of tunnels dug by forced Indonesian labour under Japanese occupation from 1942 as a bunker and store, now partly open with the ammunition rooms, kitchens and ambush points shown. Bukittinggi above is the Minangkabau highland town with its clock tower and market.

What you actually see

• A tectonic rift valley - the Sumatran Fault opened in the ground, not river-cut.
• The Japanese tunnels - two kilometres dug by forced labour from 1942.
• A green valley floor - paddy and river a hundred metres below the town.
• Bukittinggi above - the Minangkabau town on the rim.

When to go

All year; mornings before the cloud. Half a day.

Honest expectations

The tunnels are dim, damp and were dug by forced labour, many of whom died - the guides say so. Paths down into the canyon are steep. Viewpoints in town are crowded with vendors.

Nearby

Bukittinggi, Lake Maninjau and the Harau valley are all close.