Malbork Castle: The World's Largest Castle Built by Teutonic Knights (xataka.com)

• Covers 21 hectares, four times the size of Windsor Castle.
• Constructed by Teutonic Knights as a fortified monastery and administrative center.
• Required 30 million bricks and featured advanced medieval heating and plumbing.

"The Castle of the Teutonic Order in Malbork, Poland, is the largest castle in the world by area, covering over 30 million bricks. Built in the 13th century, it served as the headquarters of the Teutonic Knights during the Baltic Crusades. Heavily damaged in WWII, it was meticulously restored and is now a UNESCO World Heritage site, housing a museum."