In Olsztyn, there are ruins of a medieval castle, the first on the Trail of the Eagles' Nests (Szlak Orlich Gniazd) from Częstochowa - a system of medieval castles that once guarded the border of the Kingdom of Poland. Most of the castles in this area were built on hard-to-reach limestone rocks (similar to eagles' nests) of the Kraków-Częstochowa Upland (called also Polish Jura), probably by order of King Casimir the Great. The other castles I will present in future videos.