Makgadikgadi is the floor of a lake that no longer exists. A freshwater sea larger than Switzerland stood here until faulting tilted the basin and took its rivers away, leaving roughly 16,000 square kilometres of salt pan — a grey-white crust so flat that the only thing bending the horizon is the curve of the earth. Sowa and Ntwetwe are the two great pans, and from the middle of Sowa rises Kubu Island: a granite whaleback a kilometre long and ten metres high, crowned with old baobabs and strewn with dry-stone walls and hundreds of cairns left by people who came after the water was gone. To the ox-wagon traders and missionaries who crossed in the 1800s, those trees were the only landmarks in a country with no other marks.
For most of the year the pans are a moonscape: shadeless, silent, empty of everything but wind. The rains change all of it. From around December shallow floodwater spreads over the crust, grass greens the fringes, and 20,000 to 30,000 zebra walk in off the Boteti River — Africa's largest zebra migration, and one almost nobody watches. On Sowa, lesser and greater flamingos arrive in their hundreds of thousands to breed on the mud; in a dry year they do not breed at all. The dry months offer the opposite of spectacle: camp on the crust, with no settlement light for a hundred kilometres, and the Milky Way runs to a horizon that hides nothing. The western pans and the Boteti are protected as a national park, Sowa has been pumped for soda ash since 1991, and Kubu is looked after by the local community. The greatest of the beacon trees is gone — Chapman's Baobab, six fused trunks and 25 metres around, fell on 7 January 2016.