What historic castle, located on the north bank of the River Thames is famous for imprisoning people such as Clement Walker?
Clement Walker:  Author of the "History of Independency", which as a project with several editions included also his "Anarchia Anglicana", he was a strong opponent of religious factionalism, and was imprisoned in the Tower of London, where he died without being brought to trial. Tower of London: The Tower of London, officially Her Majesty's Royal Palace and Fortress of the Tower of London, is a historic castle located on the north bank of the River Thames in central London.
Tower of London