Don't miss these spectacular limestone caves, 40km southeast of Bari and Italy's longest natural subterranean network. The interlinked galleries, first discovered in 1938, contain an incredible range of underground landscapes, with extraordinary stalactite and stalagmite formations – look out for the jellyfish, the bacon and the stocking. The highlight is the Grotta Bianca (White Grotto), an eerie white alabaster cavern hung with stiletto-thin stalactites.
There are two tours in English: a 1km, 50-minute tour that doesn't include the Grotta Bianca (€10, on the half-hour); and a 3km, two-hour tour (€15, on the hour) that does include it. The temperature inside the cave averages 18°C so take a light jacket.
Visit, too, the Museo Speleologico Franco Anelli or the Osservatorio Astronomico Sirio , with its telescope and solar filters allowing for maximum solar-system visibility.
