Harzburg, Castle ruin in Bad Harzburg, Germany

Harzburg, also called Große Harzburg, is a ruined hill castle on the Großer Burgberg above Bad Harzburg, at about 482 m. Its roughly 55 × 220 m plateau was split by a 10 m deep neck ditch into an east and a west wing, now linked by a modern stone bridge. Of the square bergfried, 9.35 × 9.45 m with 3.85 m thick walls, a low section has been rebuilt; foundation fragments, the 57 m deep well and information boards remain.

Emperor Henry IV built the castle in 1065 as a stronghold during his conflicts with rebellious Saxon nobility. The fortress became a key position in the medieval power struggles between imperial and regional forces during that period.

The castle name comes from the Harz range, called Hart in Middle Low German, probably linked to hardt, "mountain forest". The site also holds the 19 m Canossa Column, put up in 1877 during the Kulturkampf for Bismarck's 800th anniversary of Henry IV's Walk to Canossa, plus a Bismarck Elm and a Krodo statue.

Well-marked hiking trails start from Bad Harzburg town center and lead up to the ruins by following signs toward Burgberg. The paths are accessible on foot at a relaxed pace, making it a straightforward walk from the lower town.

The castle well lies outside the walled area, on the north slope, and is 57 m deep; its upper shaft is nearly square, about 3 m across, and bricked to a depth of 8.15 m. A tunnel branches off at roughly 12 m, and in 1968 it was opened from the hillside over 18 m so investigators could enter it.