Llyn Brianne Dam - Featured Walk on Craig y Nos Castle's main site
Location: Llyn Brianne, including scenic circular drive
Directions: Set your sat nav to take you to Ystradffin but set it to go via Abergwesyn. Check where you are going against the map in case your sat nav does not take you on the correct lanes. This route takes you on a scenic drive with lots of views. Lanes are narrow, winding and steep in places as you drive through deep valleys with sheer drops on one side of the road, and several blind bends and summits.
The route takes you through a series of valleys and forests and up some steep hills with switchback roads, until eventually you see the waters of Llyn Brianne before you. There are some nice stopping spots along the shore before you get to the dam itself. The drive around the reservoir alone is several miles long.
Before you get to Ystradffin you will see a sign to Llyn Brianne Dam, where you can park up in an area that used to be a quarry (presumably providing the material for the dam). You can then walk over the Dam and around the side of the Llyn Brianne reservoir. This is a nice dog walk and includes some forest trails. However you cannot walk all the way around the dam. It is huge. So this is not a circular dog walk.
I noticed sheep sometimes get on to the dam path from the fenced in mountain grazing above, so keep an eye on dogs running too far ahead off the lead in case they put up a lone sheep.