Burg Eisenhardt, Medieval castle in Bad Belzig, Germany.

Burg Eisenhardt is a fortress on the Bricciusberg at the southwestern edge of Bad Belzig. Its irregular seven-sided ring wall has roundels at the corners, and the round keep in the courtyard, 28 metres high, was built of fieldstone in the early 13th century, with red brick renewing its northwest outer walls in 1859. The gatehouse to the south was built in the 15th century as a double-tower gate and faced with brick.

Belizi was first documented in 997 as a burgward transferred by Emperor Otto III to the Archdiocese of Magdeburg. Around 1305 Duke Rudolf I expanded the castle and walls, and in 1358 Belzig received town rights. From about 1477 the Wettins rebuilt it as a fortress with rondelles for handguns and medium artillery, possibly designed by Arnold von Westfalen. Swedish troops damaged it in 1636; renewal began in the 1680s and Johann Georg III reconsecrated it in 1691.

Since 1998 the band Keimzeit, founded in Bad Belzig, has played open-air concerts in the castle courtyard each summer. The courtyard also holds a local history museum, a registry office branch and a library focused on the castle's history.

The castle sits on a hilltop and involves some climbing to reach, though the paths are well-maintained and pass through wooded surroundings. Inside and around the complex you can find different areas to explore, with special events occurring seasonally.

The keep's lower level served as a dungeon, while its middle floor held a round-arched entrance, a latrine niche and a fireplace. In 1859 its northwest outer walls were rebuilt in red brick, contrasting with the original fieldstone.