The Cow Tower
Open accessfree to visit at any reasonable time
Substantial ruinsruined, but plenty survives above ground
The Cow Tower is an artillery fort in Norfolk. It is the only artillery fort the Albion Guide charts in the county. Norwich Castle and Horsford Castle are among the castles within 7.3 km. The nearest railway station, Norwich, is under a kilometre away.
More at the National Heritage List entry