The castle from the 14th century, located on the Trail of the Eagles' Nests, stands in a place whose first inhabitants were Neanderthals, and under the castle hill there is a complex system of caves. The castle, built by Casimir III the Great, protected the western border of Poland against the attacks of Silesian princes and the army of Archduke Maximilian Habsburg in 1587. Destroyed by the Swedes during the Deluge in the 17th century, it was never rebuilt. There's a quest (treasure hunt) available in the location.
Zamkowa 3, 42-256 Olsztyn
Source - References