Tretower Court and Castle sits west of Crickhowell and adds a more substantial historical stop to a day in the Usk Valley. The site combines the remains of a small castle with a later medieval court house, so you get both defence and domestic life in one visit.
It is especially useful if the weather is too poor for a long hill walk. Pair it with Crickhowell's centre and bridge for a quieter, history-led day.