In which country is the largest castle in the world measured by land area?

The Castle of the Teutonic Order in Malbork is located in the Polish town of Malbork, is the largest castle in the world measured by land area.

It was originally built by the Teutonic Knights, a German Roman Catholic religious order of crusaders, in a form of an Ordensburg fortress. The Order named it Marienburg (Mary's Castle). The town which grew around it was also named Marienburg. In 1466, both castle and town became part of Royal Prussia, a province of Poland. It served as one of the several Polish royal residences, interrupted by several years of Swedish occupation, and fulfilling this function until Prussia claimed the castle as a result of the First Partition of Poland in 1772. Heavily damaged after World War II, the castle was renovated under the auspices of modern-day Poland in the second half of the 20th century and most recently in 2016. Nowadays, the castle hosts exhibitions and serves as a museum.

The castle was expanded several times to house the growing number of Knights. The castle has several subdivisions and numerous layers of defensive walls. It consists of three separate castles - the High, Middle and Lower Castles, separated by multiple dry moats and towers. The castle once housed approximately 3,000 "brothers in arms". The outermost castle walls enclose 21 ha (52 acres), four times the enclosed area of Windsor Castle. The developed part of the property designated as a World Heritage Site is 18.038 ha (44.57 acres).