Hanstein Introduction, 2
The first mention of Hanstein Castle names it as one of the possessions of Otto Count of Northeim and Duke of Bavaria. It was destroyed in 1070 by King Heinrich IV - I've mentioned in this post, that the relationship between Otto and Heinrich was an uneasy one since Otto was one of the major players in the Saxon opposition against the king.
The conflict started by an intrigue when a certain Egino accused Otto of planning to murder King Heinrich. I'll get back to events that surround the accusation and Heinrich's and Otto's reactions. What is clear is that in 1070 things had gone downriver really bad; Otto and his friend Magnus Billung had forfeited all their allodial possessions and fiefs and been proclaimed outlaws.
Trench between inner and outer curtain wall
The Hanstein, then still a wooden castle with probably only one moat and curtain wall, was destroyed by King Heinrich during what one website refers to as Battle of Eschwege. I researched that and it turned out it was a skirmish at best and not immediately connected with King Heinrich IV's actions. In September 1070, Otto of Northeim fought against a certain count Ruotger or Rugger who held land in the Eschwege area, commanding a troop of Thuringians. No siege is mentioned, so the Hanstein probably wasn't involved in that particular conflict. Nor do I think a minor troop would have had the siege engines necessary to conquer a place as well fortified as Hanstein Castle.
Otto won that one, but it didn't really change his situation, which was rather desperate at the time. Also, Ruotger seemed to have escaped, if he's the same mentioned five years later in connection with a transaction involving the Eschwege earldom. Sabine Borchert, Herzog Otto von Northeim, Hannover 2005.