The hills behind Rimini hide a surprising piece of geology. Around the hamlet of Onferno, in the comune of Gemmano, the ground is made of gypsum, laid down when the Mediterranean dried out millions of years ago and then pushed up into these ridges. Water dissolves gypsum easily, so the landscape is pocked with sinkholes, blind valleys and caves, and the Grotta di Onferno winds for hundreds of metres beneath the village. The name is often linked to inferno, supposedly because vapour rising from the cave mouth in cold weather looked like the breath of hell.
The cave is the heart of a regional nature reserve and shelters a large colony of bats, several species of them, which pour out at dusk in summer. Guided visits run through galleries of glittering gypsum crystals and odd formations, cool even in August. Above ground the reserve is a patchwork of oak woods, scrub, meadows full of orchids in spring and abandoned terraces. In September 1944 these quiet ridges were the scene of savage fighting on the Gothic Line, when British troops battled for days to take Gemmano, and the area is sometimes called the Cassino of the Adriatic.
For riders, the Valconca behind the Adriatic Riviera is a fine playground, ignored by most of the beach crowd below. Narrow roads climb from the Conca valley through Mercatino Conca, Montescudo and Gemmano, with tight bends, steep pitches and sudden views of castles on hilltops: Montefiore Conca's fortress is close, and San Marino's three towers loom on Monte Titano just to the north. The tarmac is patchy in places and gravel collects on bends after rain. Spring and early autumn are perfect; summer weekends bring more traffic as people escape the coast.
Morciano di Romagna, nine kilometres away, is the nearest proper town with fuel, shops and a market. The hill villages have a bar or two, and the piadina, the flatbread of Romagna filled with ham, squacquerone cheese and rocket, is the obvious lunch. If you visit the cave, bring a light jacket, and note that visits are guided and timed, so check before you plan around one. Rimini's beaches and nightlife are only half an hour away if the evening needs livening up.