This is one of the more unusual features of Carisbrooke Castle on the Isle of Wight. This comes from a British Pathe news bulletin of 1963. The castle was placed under state guardianship and is now part of English Heritage.
The well was dug after 1136, and is some 49 m deep. The first recorded mention of the use of donkeys to turn the wheel dates to 1696.
A more recent video from the BBC shows the revised conditions in 2011, although some of the older Ministry signage can still be spotted.