Some 32km up the Esino valley from Jesi, just after the Gola di Rossa, a road leads up from Genga train station to the Frasassi gorge, carved by the River Sentino, which was also responsible for creating the 18km of caves beneath it. The largest of the Grotte di Frasassi, or Frasassi caves, was discovered only in 1971, and just over a kilometre of its caverns and tunnels is now open to the public on tours that last seventy minutes – note that the average temperature inside is 14°C.

Inevitably, the most remarkable stalactite and stalagmite formations have been named: there’s a petrified Niagara Falls, a giant’s head with a wonderfully Roman profile, a cave whose floor is covered with candles complete with holders, and a set of organ pipes. The vast Cave of the Great Wind, at 240m high, is one of the biggest in Europe – large enough to contain Milan Cathedral – and over the years has been used for a series of experiments, ranging from sensory deprivation (as a possible treatment for drug addicts) to a subterranean version of Big Brother.

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