The Marienburg Castle is a Gothic revival castle in Lower Saxony, Germany. It is located 15 kilometres (9.3 mi) north-west of Hildesheim, and around 30 kilometres (19 mi) south of Hanover, in the municipality of Pattensen, Hanover. It was a summer residence of the House of Guelph. It was once given as a birthday present by King George V of Hanover (reigned 1851–1866) to his wife, Marie of Saxe-Altenburg.