Penrith Castle was built by Ralph Neville, the 1st Earl of Westmorland, shortly after he became owner of the Manor of Penrith in 1396. The castle and Ralph Neville himself played a vital part in defending the Border and surrounding areas from the Scottish, and this gave Neville a powerful and influential position in the Cumbria area. After his death in 1425, Penrith Castle past on to Ralph's son, Richard Neville, who used the site as his headquarters, improving its defenses and building the castles famous 'Red Tower', before passing it on to his son (again named Richard). Then in 1471 Penrith Castle was passed to the soon-to-be King Richard III, who lived there for the next 12 years and carried out extensive revamps and changes, in order to make it 'a suitable residence'. These changes included replacing several windows with much larger versions (to allow more light into the castle), and the construction of a new gatehouse and tower.
However, after Richard was officially crowned King in 1483, the castle was hardly used again (except briefly in 1648, as John Lamberts headquarters during the Civil War), and by the 16th century it was falling into decay and much of it had been dismantled.
The Castles Park was created in 1920, and these days the public can visit and explore Penrith Castle for free.