Malbork Castle

In 1457, King Casimir Jagiellon ceremonially entered the castle in Malbork, which remained in the Kingdom of Poland for over 300 years.

An excerpt from the article 24 facts about Malbork Castle

Malbork was a royal castle, the king's temporary residence, and the banner of the Kingdom of Poland flew over it, although daily, the king was represented at the castle by the starosta of Malbork (an elder administrator). The castle encompassed the adjacent lands, especially Żuławy (Vistula Fens).