Bathurst Basin in Bristol. The two storey pink Georgian building has a plaque on the wall indicating that for 462 years, between 1373-1835, this spot was part of the boundary between Gloucestershire and Somerset. The Bathurst Basin, leading to the Avon New Cut, would have been familiar to those who sailed on the Kennersley Castle. It was named after Charles Bathurst, the Bristol MP, not Lord Bathurst.
Photo by Thomas Nugent (CC BY-SA 2.0)