Rocca Ubaldinesca, Renaissance fortress in Sassocorvaro Auditore, Italy.

Rocca Ubaldinesca is a brick fortress in the Marche region featuring a distinctive turtle-shaped layout with an internal courtyard rising prominently above the Foglia River valley. The structure was designed to function as both a defensive stronghold and a commanding presence over the surrounding landscape.

Built around 1475, the fortress was commissioned by Federico da Montefeltro, Duke of Urbino, from his architect Francesco di Giorgio Martini, early in Martini's service as ducal military engineer. It passed to the Duke's brother Ottaviano degli Ubaldini della Carda, whose heraldic symbols remain in the castle. After 1511 it belonged to the Doria family of Genoa, counts of Sassocorvaro; the line died out in 1626 and the territory passed to the Papal States.

The castle's name comes from Ottaviano degli Ubaldini della Carda, brother of Duke Federico da Montefeltro, whose heraldic symbols remain in the building. Local lore links the turtle-shaped plan to alchemy, and the fortress now houses a library of esotericism and an alchemy laboratory with alembics and instruments of the Great Work. A small theatre carved from one of the largest halls opened to the public in 1860.

The fortress stands at the centre of the hilltop village of Sassocorvaro, above the Foglia valley; the approach is on foot through the village streets. Inside, the small courtyard and the rooms of the former theatre and library are visited on foot, with steps between levels. The building is a museum, so check opening arrangements before climbing up.

During World War II the fortress sheltered more than 10,000 artworks from different Italian cities, protecting them from wartime destruction. This role as a storage vault earned it the nickname 'Ark of Art'.