Three days in Uyuni: the biggest salt flat on earth, and a town that exists only to reach it

Whether you have flown in or come off a night bus, the first day is a half day. There are exactly two things in Uyuni and both are about the railway.

The train graveyard sits three kilometres southwest of town on the old line, and it is a row of steam locomotives and rolling stock left standing on the salt pan since the mining traffic dried up in the middle of the last century. Most of them were built in Britain and shipped up from the Pacific coast. They have been stripped of anything removable and are now rust-red skeletons in the wind, and people climb all over them, which nobody stops. Go in the late afternoon, when the light is low and the tour groups have gone.

Back in town, the railway and archaeology museum behind the station is small, dusty and cheap, and it explains why a town exists here at all: this was the junction where Bolivian minerals turned towards the sea, and the reason the tracks were laid is the same reason the locomotives were abandoned.

The day tour leaves mid morning and the first stop is Colchani, a village on the edge of the flat where salt is scraped up, piled into cones to drain and dried in a shed. There is a small museum of salt carvings, a strip of stalls selling salt and llama wool, and the first sight of the white plain running off behind it.

Then you drive out onto it, and the scale immediately stops making sense. The surface is white, dry and cracked into hexagons, there is nothing on the horizon in any direction, and with no object of known size in view the eye gives up. This is why every driver carries a bag of props and every group spends half an hour making photographs of somebody being eaten by a dinosaur. Let them; it is genuinely funny and it is also the only way to record how flat the place is.

Lunch is usually taken at Isla del Pescado, an outcrop of fossilised coral rising out of the salt and covered in giant cactus, some of them ten metres tall and growing about a centimetre a year. There is a path to the top and a small fee. In the wet season the tour becomes something else entirely: a few centimetres of standing water turn the whole salar into a mirror, and the drivers know exactly where to park for the reflection at sunset.

Pulacayo is twenty minutes up the road towards Potosí and almost nobody stops there, which is the point. It grew around the Huanchaca silver mine, once one of the richest in the world, and when the ore ran out the town emptied and was left more or less standing.

What is there now is the wreckage of an industrial age at 4,000 metres: mine buildings, machinery rusting where it stopped, and Bolivia's first railway with its locomotives still on the rails. One of the carriages is displayed as the train held up by Butch Cassidy and the Sundance Kid, who were killed not far from here shortly afterwards. A local guide will usually appear and show you round for a small fee, and it is worth taking.

That leaves the afternoon for the bus or the plane. Potosí is a few hours east on a decent road, La Paz is an overnight haul, and the flight north takes an hour.