The Semi-Lunar Tower is one of the surviving pieces of Waterford's medieval city defences, named for its half-moon plan. Waterford once had a much larger circuit of walls and towers controlling the Viking and Norman port; today the fragments are scattered through the modern city, sometimes obvious, sometimes half-hidden in schoolyards and side streets.
This is a modest stop, but a useful one if you are tracing Waterford beyond Reginald's Tower. The pleasure is in assembling the old defensive line from fragments: a tower here, a stretch of wall there, and the realisation that the compact city centre still follows older boundaries than its shopfronts let on.