S1, E2: Paul visits Cragside House in Northumberland, home to one of Victorian Britain's least remembered inventors, Lord William Armstrong, who paved the way for domestic electricity. Charlie Luxton spends the night in Lincoln Castle, in a 19th century prison that was closed down 130 years ago; Clare Balding travels to North Yorkshire to visit one of the country's most beautiful and obscure ruined abbeys, and guest reporter Charley Boorman uncovers the sunken remains of Britain's very first submarine.