Blaubeuren, Germany: the blue spring and Gothic abbey at the foot of the Swabian Jura

Behind the old abbey of Blaubeuren wells up one of Germany's strangest natural wonders: the Blautopf, a karst spring whose deep funnel glows an almost luminous blue. The colour, which shifts with the light, comes from sunlight scattering off countless tiny limestone particles suspended in the water - the same physics that turns the sky blue - and the pool's true depth long defied measurement, feeding local legends of a water nymph called the Beautiful Lau. A small town of around 12,500 people in Baden-Württemberg, Blaubeuren lies at the foot of the Swabian Jura about 20 kilometres west of Ulm and roughly 80 kilometres south-east of Stuttgart.

Beside the spring stands Blaubeuren Abbey, a Benedictine monastery founded in 1085 and rebuilt in late-Gothic style around 1500. Its church holds a magnificent carved and painted high altar and choir stalls by the Ulm school, while the adjoining monks' bathhouse is the only one of its kind preserved in Germany.

An old town of timber and water

The little town that grew up around the abbey keeps a centre of half-timbered houses threaded by channels of the clear Blau river, with a medieval town hall and former hospital among its landmarks. The whole valley sits within the karst country of the Swabian Jura, its slopes riddled with caves.

The oldest art in the world

Those caves have made Blaubeuren famous far beyond its size. In the nearby Hohle Fels archaeologists found the Venus of Hohle Fels, a mammoth-ivory figurine carved around forty thousand years ago and counted among the oldest known works of figurative art, along with one of the earliest musical instruments. The finds are shown in the town's prehistory museum, and the caves themselves form part of a UNESCO World Heritage Site inscribed in 2017.