Here you can visit the site of the infamous battle of Flodden Field, where the Earl of Surrey defeated and killed James IV of Scotland. There is a fantastic open air ecomuseum, which encompasses around forty sites that were involved in the battle in some way. At Flodden Hill you can discover the area in which the Scots camped, follow the Flodden Battlefield Trail, visit the Flodden Peace Centre and the memorial. There are lots of other sites of interest contained within the ecomuseum, which were of importance to the battle itself, from churches and keeps to huge castles and ports.
Set high above the River Tees, Barnard Castle has played a big role in the history of not only the North of England, but of the UK too. It was built in the 12th Century, was home to Richard III and played a part in the Northern uprising during the reign of Henry VIII. It features an impressive round keep and even a sensory garden for the visually impaired, although that's a more recent addition of course. Now largely in ruins, some of the masonry was used to extend the nearby Raby Castle.
Tynemouth Priory and Castle
Located on a rocky headland overlooking the North Sea and the River Tyne, the castle and the priory at Tynemouth form what was once one of the most heavily fortified areas in the North of England. The early kings of Northumbria were buried here at the priory, yet it was attacked by the Danes and abandoned. A monastery was later built on the site, but again it suffered at the hands of Henry VIII's reformation and only the remains can be seen today.
There has been a castle on the site since before 1095 - the original was of course built from wood and mud, however what remains today is the fortress built in medieval times. It's had many guises over the years, with the remains of the stronghold being used to house a lighthouse, barracks and most recently the local coastguard station, so it has certainly had a varied past.