This is, or rather was, the castle in Pontefract, Yorkshire,
England.
So why demolish it?
Because the residents of Pontefract in 1649 were rather sick of soldiers camping on their land whilst trying to clear the castle of the dreaded Royalists. When the Royalists finally surrendered after three sieges spanning over four years the residents petitioned parliament to demolish the castle so no one else could use it as a fortress.
These pages tell the story of Pontefract Castle.