Nant Tarw consists of two circles, a larger and smaller one, which are both are made up of about eighteen remaining small stones. There are a number of larger fallen stones near the circles, plus a separate group of stones near the largest circle. The site is located off the A40 at Trecastle between Brecon and Llandovery. The road leads to the Usk Reservoir and forestry plantation.
Our Visit
We went to this site just before visiting 'Y Pigwyn'. Taking the road to the left as you leave Trecastle just before the Antiques Centre. Go past the Roman Road that leads to Y Pigwyn and follow the road that leads up to the Usk Reservoir. The two circles and cairn are to the south of the reservoir and plantation. The road to the reservoir is narrow so care needs to be taken. The picture of the Usk reservoir was actually taken from the Roman Road looking south close to Y Pigwyn.