Fort III in Kaliningrad, Military fortification in Kaliningrad, Russia.

Fort III is a military fortification in Kaliningrad, Russia, made up of thick brick walls, concrete structures, and a system of ditches and casemates. The layout is typical of 19th-century defensive engineering, with earthen ramparts, underground passages, and several layers of defensive positions arranged around a central courtyard.

Built between 1873 and 1878, Fort III was the first of Königsberg's twelve main forts to begin construction and the largest, originally named Kwednau after the hill it stood on. In 1894 it was renamed King Frederick III. It guarded the railway lines to Rauschen and Kranz and the road to Kranz. On 9 April 1945 it was taken by the 557th Rifle Regiment of the 153rd Rifle Division, suffering only minor damage.

The fort's name changed over time: it was first called "Quednau" after the hill it stands on, and only from 1894 bore the name of King Frederick III. The site is closed to visitors, with a sign at the gate reading "Object closed for restoration"; since February 2024 it has been leased to a commercial firm for restoration and conversion into a tourist facility with a hotel.

Access to the fort grounds was closed as of July 2016, with a sign at the gate reading "Object closed for restoration". In February 2024 the fort was handed to a commercial organisation for restoration and conversion into a tourist facility with a hotel, and construction work is under way. Check locally before travelling, since the site is a working construction zone.

The fort's original name was "Quednau", after the hill it was built on; it only received the name "King Frederick III" in 1894. Its dry moat, 10–11 m wide and 6 m deep, let the troop barracks be built on two levels. Access was closed for restoration as of July 2016, and by February 2024 the fort had been handed to a commercial firm for conversion into a tourist site with a hotel.