Château de Regnéville, Medieval castle ruins in Regnéville-sur-Mer, France.

Château de Regnéville is a medieval castle ruin located on the Normandy coast. The keep rises about 20 meters high with walls over 3 meters (10 feet) thick, positioned at the northeastern corner of the upper courtyard.

Founded in the 12th century, the castle was held by the kings of Navarre from 1349, when Charles the Bad inherited his father's Norman lands. In 1378 French troops took it, and in 1418 the Duke of Gloucester seized it for England. Retaken in 1449, it was razed in 1637 after Louis XIII ordered the demolition of fortifications not on the kingdom's borders.

The castle's name comes from the village of Regnéville-sur-Mer, whose dry harbour it guarded; the harbour was among the busiest of the Cotentin from the Middle Ages until the 17th century. In 1364 Charles the Bad's supporters strengthened the fortifications, and the spiral staircase in the keep was rebuilt in the 16th century and is still visible. The lords of Piennes lived here until the 18th century.

The ruins stand beside the church on the edge of the Sienne estuary at Regnéville-sur-Mer. Excavations from 1991 to 1993 uncovered the foundations of the upper courtyard, and restoration has continued since 1994, so some areas may be fenced off. The keep's 16th-century spiral staircase is still visible inside the tower.

In the mid-19th century Victor Bunel set up a mechanical sawmill for cutting marble in the former lower courtyard. The keep itself was packed with powder and blown apart in 1637, splitting from top to bottom along its spiral staircase.