Ploty Old Castle, Medieval castle in Płoty, Poland

Ploty Old Castle is a stone fortress in the Polish town of Płoty featuring a four-story defensive tower surrounded by a moat. The preserved defensive walls date from the 13th century and form a substantial part of the structure.

The first defensive structure on the site was a 12th-century stronghold on the Rega. In 1277 Dobiesław Wotuch, a knight of Barnim I, built a four-storey stone-and-brick tower measuring 12.7 by 17 metres on a 28 by 36 metre platform ringed by a moat. In 1465 Kołobrzeg townsmen sacked and ruined it; the von der Osten family rebuilt it with a three-storey wing in the south-east corner. From 1577 the Blücher family converted it into a Renaissance residence.

The ground-floor chamber, now called the Knights' Hall, has richly decorated vaults and a large architectural fireplace; the Renaissance door of this room was reconstructed after the war. A chamber in the north corner holds a Mannerist architectural fireplace. Two plaques on the facade mark the castle's rebuilding from the Social Fund for the Reconstruction of the Capital and the 70th anniversary of the Płoty public library (1947–2017).

The fortress is located at Zamkowa 2 street and now houses a municipal library and social welfare center. The interior is not open for visits, but you can view the outer structures and fortifications from the outside.

The medieval tower survives only in its lower storeys, together with a stretch of the stone perimeter wall; the rest was rebuilt between 1959 and 1967, when original wall paintings inside were destroyed. Two plaques on the facade mark the reconstruction from the Social Fund for the Reconstruction of the Capital and the 70th anniversary of the public library (1947–2017).