The Empty Quarter crossing

Riyadh is the country's main air hub, so it is the usual arrival point. You are met and taken to your hotel. Nothing is scheduled for the rest of the day; the expedition briefing is tomorrow evening.

The morning is at the National Museum of Saudi Arabia, where the halls run in order from geology and prehistory through pre-Islamic Arabia to unification. It is worth the time: the rest of the country reads differently afterwards.

In the afternoon you walk a stretch of Wadi Hanifa, the valley that runs the length of the city and carried the water Riyadh grew on, reclaimed from a dumping ground into a chain of parks, paths and treated water channels. The expedition briefing and a full kit check are in the evening.

The Tuwaiq escarpment runs some 800 km across central Arabia. About 100 km north-west of Riyadh it breaks off at the point known as the Edge of the World, where the wall falls away to a flat desert floor that carries on to the horizon with nothing on it. The rock holds marine fossils, snails and shells, because this was seabed long before it was desert.

Sunrise and sunset are the two times worth planning around, both for the light along the cliff and because the middle of the day is exposed and hot. The final approach is rough track and needs four-wheel drive, and there is no water, food or fuel at the site and mobile coverage drops out, so everything is carried in. It is also a useful shakedown for the vehicles before the south.

A long driving day south from Riyadh to the edge of the sand sea. The last stretch leaves tarmac; tyres are let down and the convoy sets the first camp before dark. Cooking, water and bedding are the crew's job, not yours. From here on there are no fuel stops and nothing to buy.

The day is spent inside the reserve, on the ground where the dunes of the Rub' al Khali run up against the Tuwaiq escarpment. That combination - sand sea on one side, rock plateau on the other - is why it qualified as a natural listing rather than a cultural one.

This is where the Arabian oryx was returned to the wild after going extinct outside captivity, and the reserve now holds oryx along with sand gazelle and mountain gazelle. Sightings depend on the day and are not promised; the driving is timed for early and late, when there is most chance of them and least heat.

A second full day in the dunes, further out from the escarpment and into ground where there is genuinely nothing. The dunes here run to enormous scale and the driving is slow. The turn north begins in the afternoon and the last camp is pitched back near the desert edge. This is the night to stay outside after dark rather than in the tent.

The drive back to the capital, tyres brought back up at the tarmac. You are transferred to the airport for your flight out. If your flight is late in the day a day room can be held so you can shower and repack after three nights in the sand.