A 15 m granite wave frozen mid-break in the Western Australian wheatbelt, streaked in rust and grey, on the flank of a rock older than most continents.
A basalt "organ" of up to 12 m columns exposed by an old quarry in northern Bohemia, the oldest protected geological site in the country.
A stretch of the São Miguel river where grey quartzite has been polished into craters, pools and lunar curves.
A 90 km canyon in the steppe east of Almaty, whose Valley of Castles is a corridor of red sandstone towers eroded into turrets and arches.
One of the longest cave systems in Africa, where the Weyb river disappears into limestone and emerges 1.5 km later through a hall of columns, and a Muslim pilgrimage site for centuries.
The lowest point in Africa, a lake ten times saltier than the sea, ringed by a blinding crust of salt and black lava at the bottom of the Afar rift.
The Eye of the Sahara: a 40 km bullseye of concentric rock rings in the Mauritanian desert, visible from orbit and almost invisible from the ground, which is exactly why hardly anyone goes.
A narrow gorge in the Gobi where a field of ice survives most of the summer in the shade of 200 m walls, with lammergeiers overhead and pikas underfoot.
A salt-dome island in the Strait of Hormuz whose soil comes in seventy colours, with a red beach that stains the sea, rainbow valleys and a 16th-century Portuguese fort.
Caverns of swirled blue-and-white marble carved by waves into the shore of General Carrera lake, reached by small boat from a village on the Carretera Austral.
One of the highest fortresses in the Apennines: a roofless 10th-century watchtower and ring walls on a bare limestone ridge at 1,460 m, free and open day and night.
The mud-brick remains of the medieval trade capital that funnelled Saharan gold to the Mediterranean, now a field of eroded walls outside Rissani that nobody guards.