Canyon Rio Sass, Canyon in Fondo, Trentino, Italy

Rio Sass Canyon is a 300-metre-long gorge up to 60 metres deep in Fondo, in the Alta Val di Non. The Rio Sass, an iron-rich spring, runs between vertical walls that narrow to 25 centimetres and open to about 30 metres, dividing the village in two. Along the route are thin waterfalls, stalactites, stalagmites, giant's kettles, red and green algae colonies and fossils.

The gorge became accessible to visitors in 2001 when local authorities installed metal walkways and stairs throughout the passage. This development marked the beginning of tourism at the site and opened its interior to the public.

The stream that runs through the gorge is a ferruginous spring, and the canyon splits the village of Fondo in two. Near the end of the descent stand the remains of the old Bagni di Fondo spa, active from the mid-19th to the mid-20th century; tradition holds that Emperor Franz Joseph and his wife Sissi stayed there.

The route starts beside the town hall at the Smeraldo cooperative, where helmets and waterproof capes are issued at the "casa dell'acqua"; sturdy clothing is advised. Visits run from mid-April to mid-November and must be booked in advance. The path is equipped with suspended walkways, steps and ladders, and is covered in both directions, descending and climbing about 600 steps twice in roughly two hours.

The rock walls are covered with colored algae patterns and moss layers that grow in the damp, shadowy environment. These living coatings create natural art patterns on the stone and shift with the seasons and changing light.