Funded by the vast profits from the slate mine of Caribbean sugar-plantation owner and anti-abolitionist Baron Penrhyn, and extended and embellished by his great-great-nephew, this immense 19th-century neo-Norman folly is both tasteless and spectacular. Flanked by a Victorian walled garden, the creeper-clad stone walls of the Norman 'fortress' embower the neo-Gothic hall with its darkly extravagant rooms, complete with intricately carved ceilings, stained-glass windows, opulent furniture and even early flushing toilets. 'Early birds' can book free castle tours (10.30am to noon).
Also notable are the on-site industrial railway museum and Llandygai village, a model settlement for Penrhyn's quarry workers that abuts the estate walls. Penrhyn is 1.5 miles east of Bangor, off the A5; buses to Llandudno stop at the gate.