The Northumberland estate of Cragside was made famous when it became the first house in the world to be lit by hydro-electricity.
Now it is going back to being powered by water again.
And the equally famous Northumberland actor, Robson Green, was the man to switch the power back on.
The modern hydro system is a 17-metre Archimedes screw, an old system used to generate power.
It can generate around ten percent of the electricity the property needs.