Rare natural formations: basalt columns, sinkholes, painted deserts, hidden gorges. 17 so far.
A cliff of hexagonal basalt columns hanging over the Azat River, curved like organ pipes, a short scramble below one of Armenia's most visited temples.
A limestone plateau eroded into a stone city of stacked discs and mushroom pillars, an hour from the Costa del Sol and seen by almost none of its visitors.
A limestone sinkhole 600 m from the sea, filled with turquoise water where fresh and salt water meet, with steps down from a free municipal park.
Twisted columnar basalt formations, the roots of old volcanic craters, scattered along the Jökulsá canyon, where the wind and river echo off the rock.
A near-perfect natural cone rising 120 m from the white floor of the Arizaro salt flat in the high Puna, so symmetrical it looks built.
A badlands of hoodoos, petrified logs and mushroom-capped rock in shale the colour of ash, with no trails and no signs.
Hundreds of rounded granite boulders, some balanced improbably on others, scattered across a shallow valley in the middle of the Northern Territory.
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.