Bardenas Reales is a desert of pale clay dropped into the middle of Navarre, 41,845 hectares of it, with nobody living inside. Barely 300 millimetres of rain reach the Bardena Blanca in a year, and almost nothing grows to bind the ground. The cloudbursts that do arrive keep cutting the soft clay, silt and gypsum into ravines, serrated ridges and lone towers called cabezos. The best known of them is Castildetierra, a clay column capped by a slab of hard sandstone, standing by itself on open ground. Out on the dirt tracks the silence is the first thing you notice: beige running to the horizon, cracked earth, and these shapes rising out of it. Game of Thrones filmed its Dothraki Sea here, which says how little the place looks like Spain.
Light is what changes it. At sunrise and sunset the sun comes in low and sideways, every gully fills with shadow and Castildetierra glows red-gold; midday flattens the desert into glare. It is a working landscape rather than a wilderness. Some 80,000 sheep are walked down from the Pyrenean valleys of Roncal and Salazar each September to graze here through the winter, and the jets from an air force range inside the badlands are part of the soundtrack. Navarre made the Bardenas a natural park in 1999 and UNESCO named it a Biosphere Reserve the year after. Castildetierra itself is coming apart. A crack has opened at its crown, it now stands behind a fence, and it has been laser-scanned in three dimensions so that it could be rebuilt exactly as it stood if it falls. The tracks close when heavy rain turns the clay to paste.