Rain that falls on the Nullarbor does not run off; there are almost no rivers here. Instead it sinks through the porous limestone, and over millions of years it has dissolved the rock into a honeycomb. The reserve and the adjoining Nullarbor National Park together protect the world's largest semi-arid karst cave system - sinkholes that drop without warning from the flat ground, and chambers that open into darkness far below the surface. Some hold underground pools and rivers, home to blind, pale creatures - crustaceans, spiders and beetles - that have adapted to live their whole lives without light. Many of these caves and the country around them hold deep cultural significance for Aboriginal people, whose connection to this land long predates any map of it.

The reserve's northern edge is one of the strangest borders in the world: the Trans-Australian Railway, which here runs dead straight for 478 kilometres without a single curve - the longest stretch of straight railway track anywhere on the planet. Strung along that line are the names of places that barely exist - Hughes, Denman, Fisher, O'Malley, Watson - abandoned or near-abandoned railway settlements that once kept the trains running across the void. To the south the land falls away at the Bunda Cliffs, where the limestone meets the Great Australian Bight in a wall of rock 60 to 120 metres high, an unbroken rampart against the Southern Ocean. From the cliff edge in winter, southern right whales can be seen calving in the water below.

Nothing about the Nullarbor invites soft living, and the animals that endure here have made hard bargains with the heat. The southern hairy-nosed wombat digs deep, cool burrows in the sandy ground and waits out the worst of the day below the surface, emerging to graze the bluebush at night. Red kangaroos and dingoes range the open plain. The vegetation is low and tough - chenopod shrubland, the grey-green bluebush and saltbush that can stomach salt and drought and give the plain its muted, silvery colour. Classified as an IUCN Category VI protected area, the reserve is managed to keep this stark ecosystem intact while allowing traditional and sustainable uses of the land.

The reserve sits inside a complicated mosaic of country. Its corners brush against the Yalata Indigenous Protected Area and the Maralinga Tjarutja Aboriginal lands to the south and north - country that carries the long memory of the Anangu and other Western Desert peoples, and the more recent scars of the railway and the nuclear-testing era beyond. To the east it adjoins the Yellabinna Regional Reserve; to the west, the dead-straight surveyor's line of the South Australia-Western Australia border. The northeastern corner holds Ooldea, a place of profound importance and sorrow in Aboriginal history, and the railway settlement of Cook. The Nullarbor reads as empty only to those passing through; for those who belong to it, it is anything but.