Unmonetised, open-access historical ruins, castles and ancient watchtowers. 17 so far.
Three mud-brick fortresses from the 4th century BC to the 7th century AD on a hill above the Kyzylkum desert, the largest of the Khorezm desert castles and still without a ticket office.
The stone shell of Costa Rica's oldest church, built in the 1690s and abandoned after floods in 1833, standing in a lawn of coffee bushes above the Cachí reservoir.
A 12th-century castle ruin on a limestone spur 200 m above the Rhône, opposite Valence, with a walled ghost village inside its outer wall and a view down the valley to the Alps.
A deserted Byzantine village stacked on a cliff in the hills of Chios, emptied after the 1822 massacre and never resettled, its stone houses now indistinguishable from the rock.
The earthworks of the Māori fortress that ended the Northern War in 1846, a hilltop of trenches, rifle pits and palisade lines whose design anticipated trench warfare by seventy years.