Streams passing through caves on the Mendip Hills, including Thrupe Lane Swallet and Viaduct Sink (approximately 5 kilometers east of the city), emerge at Saint Andrew's Well in the garden of the Bishop's Palace, from where the water fills the moat around the Palace and then flows into Keward Brook, which carries it for approximately a mile west to the point where the brook joins the River Sheppey in the village of Coxley.