Otočec Castle, Water castle in Novo Mesto, Slovenia.

Otočec Castle stands on the largest of some 30 islets in the Krka River near Novo Mesto, on a site whose walls are dated to 1252. A southern channel was cut to form a moat, making it Slovenia's only water castle. Two wooden bridges, north and south, cross the island, and a boathouse sits on the southern channel behind the castle.

The castle was founded around 1252 and initially belonged to the de Werde family, known as the Knights of Otočec. It passed through several noble families over the centuries as regional power shifted.

The castle's name comes from the Slovene word for 'small island'; the town was renamed Otočec in 1952, when the communist government replaced the religious name Sveti Peter. Writer Ivan Tavčar set two novels, Otok and Struga and Janez Sonce, here. A local group, the Knights of Otočec, keeps the castle's knightly name alive.

The castle operates as a luxury hotel with guest rooms, a dining establishment serving regional dishes, and spaces for special events. Since it functions as a private lodging, visitors should arrange visits in advance rather than expecting casual drop-in access.

A southern channel was excavated around the original riverside stronghold to create what is now the largest island in the Krka River. This artificial moat was an ingenious defensive engineering choice that added an extra layer of protection.