Coltishall Lock, River Bure
Whilst Horstead Mill was most certainly the local "A List" playground, the adjacent lock came a close second.
The lock stopped functioning as a navigational structure in 1912, when a huge flood swept down the Bure Valley are tore out every bridge wier and lock in it's path. By the time I came to make it's aquaintance it had been converted into a manually operated sluice to carry surplus water away from the mill race. The top gates had been removed and the bottom gates replaced by two wooden guillotine paddles, bedding down onto masonry infill.