Once one of England's strongest medieval fortresses, Pontefract Castle has a history that runs through nearly every significant chapter of medieval and early modern English history. Its darkest chapter came in 1400, when Richard II — recently deposed by Henry IV — almost certainly starved to death within these walls. He was not the only notable prisoner: several others were held and executed here over the centuries, and the castle endured a long Civil War siege before being slighted by Parliament in 1649.
The ruins are well maintained and free to enter. The keep and the remains of the towers reward exploration, and the views from the highest surviving section are worth the climb. A small visitor centre explains the castle's history in detail, with particular attention to Richard II and the Civil War period. Allow an hour or so to do it justice.