Very little is left of Odiham Castle, just some earthworks and the rubble fill of part of an octagonal keep, but the pleasant walk along the Basingstoke Canal makes it worth a visit. It was built by King John between 1207-14, and was said to be one of his favourite castles. It was from this castle that he set out to Runnymede to sign the Magna Carta.

In 1216 it was captured by Louis, Dauphin of France, after a 15 day siege.

In 1236, King Henry III gave the castle to his sister, Eleanor. It became home to the de Montfort family when Eleanor married Simon de Montfort in 1238. David II, King of Scotland, spent much of his eleven year imprisonment here following his capture at the Battle of Neville's Cross in 1346. The castle was an abandoned ruin by the end of the 16th century.