Visited 5th June 2003: I asked permission to park at Caer-Arglwyddes, the farmhouse to the north west of the circle (the circle is on a public footpath so no need to ask about access). With Alfie in the baby back-pack I headed off up in approximately the right direction for the circle.
The weather was all over the place. It had been raining when I left the car, and during the walk up the hill it had cycled through a variety of conditions. The grid reference I used to get to this site is probably too far south because I got to the circle much quicker than I'd bargained for (my GPS gave me SN6965491183). The stones are very low to the ground, so it was largely luck that I found them. Up by the circle the sun came and went, and when it shone the light on the wet grass around it was beautiful.
What a tiny little thing Cylch Derwyddol is! I don't know how much stone is hidden under the soil, or how much exposed stone has been eroded away, but this site can't have consisted of anything very large when it was built. Stone circles are very unusual in Ceredigion, so I got excited about it despite the size of it. It crossed my mind that this could be a cairn kerb, but the stones are very small, and there's no sign of any cairn material (it's listed as a circle on the NMRW).
Without a Welsh-English dictionary to hand I had a go at translating the name Cylch Derwyddol and came up with 'circle of the oak meadow'. I based this on the assumption that 'derwyddol' was derived from the words 'derw' meaning 'oak', and 'ddol' meaning 'meadow'. [Judging by Tollvên's post, I got this entirely wrong].
Cylch Derwyddol lies on the eastern slopes of a mountain called Moel y Garn, which translates as 'bare or rounded mountain of the cairn'.