The old castle,Schloss Ilsenburg, lying on a high crag above the town, was originally an imperial stronghold and probably built byKing Henry I. In 995 EmperorOtto III resided inElysynaburg, whichHenry II bestowed in 1003 upon theBishop of Halberstadt, who converted it into aBenedictine monastery. The school attached to it enjoyed a great reputation towards the end of the 11th century.[3] Theabbey was finally devastated during theGerman Peasants' War in 1525.
After theReformation the castle passed to the counts of Wernigerode, who restored it and made it their residence until 1710. Higher still, on the edge of the plateau rises the Ilsenstein, a granite peak standing about 500 ft (150 m) above the valley, crowned by an iron cross erected by Count Anton vonStolberg-Wernigerode in memory of his friends who fell in theNapoleonic Wars of 1813-1815. Numerous legends cluster around this rock.[3]
Ilsenburg is betweenWernigerode (Saxony-Anhalt) in the east and Bad Harzburg (Lower Saxony) in the west through the Ilsetal. The Brocken is reachable through theHeinrich-Heine-Weg, that goes along theScharfenstein andKleiner Brocken. Ilsenburg is near theHarz National Park. To the west, there is theHarzer Grenzweg at theGreen Belt Germany, which goes along theinner German border.
The town Ilsenburg consists of Ilsenburg proper and theOrtschaften (municipal divisions)Darlingerode andDrübeck.[4] Darlingerode and Drübeck were independent municipalities until they were absorbed by Ilsenburg in July 2009.[5] Other localities within the town arePlessenburg (part of Ilsenburg proper) andOehrenfeld (part of Drübeck).