The remains of a short 18-inch (or thereabouts; I didn’t actually measure it) railway are visible by the River Ouse on the south edge of York, just upstream from the Millennium Bridge.
Here are some photos I took on April 19 2003.
The line ran through a now-blocked gateway in the wall.
A nearby noticeboard explains:
Military stores were unloaded at an Ordnance Wharf, built in 1888, and taken to the army depot in Hospital Fields Road on a narrow gauge railway, a small section of which is still visible at the southern end of New Walk. Explosives were brought in the schooner ‘Princess’ known locally as the ‘Powder boat’.