Visited 2nd August 2003: We went on to Castell Bryn-Gwyn after Bryn-Gwyn Tre'r Dryw, by which time the sun had come out again. It was lunch time, so we had a picnic on top of one of the banks. After the food William and I played rolling down the bank. This is a great place to hang out, and I'd recommend it as a picnic spot.
The Cadw sign at the entrance to Castell Bryn-Gwyn says,
The nature of this site is uncertain although it may have originally been a religious sanctuary. The earliest bank and ditch belong to the end of the neolithic period (2500-2000 BC) but the site was re-occupied and fortified in Roman times and later.
On the ground it's easy to see why everyone is so cagey about defining this site.