The castle has introduced a number of precautionary measures, including a limit on visitor numbers and social distancing rules, as well as hand sanitiser dispensers.
Built towards the end of the 13th century, Malbork Castle served as the headquarters of the Teutonic Knights for almost 150 years, until 1457.
It is one of the finest examples of a medieval fortress. In 1997, it was included in the UNESCO list of World Cultural Heritage.
A major tourist site, Malbork Castle last year attracted over 800,000 visitors, including 150,000 foreigners.