In the 11th century, the Normans built a motte-and-bailey fortification on the coast, opposite a castle in Abergwyngregyn across the Menai Strait, suggesting the castles engaged in coastal communications. Named after a local river, it was a fortified structure built on raised ground, and you can stroll through what remains of the site today.
Originally the castle was a wooden structure. Although its history is not fully documented, it faced its share of fighting, with different structures built at different times, and was later replaced by a stone structure during a civil war. Run down but restored starting in 2008, it has artfully decayed into the surrounding woodland, known as the Anglesey Area of Outstanding Natural Beauty. The area is overgrown, masking some of the features, but leaving it without too many visitors. If you visit, you may very well have the site to yourself.
Know Before You Go
The castle is open to the public year round, free of charge.
Castell Aberlleiniog is found off an unnamed road accessed from the B5109. Take the turning sign-posted to Penmon.