Joining from the Bwlch area (which is between Lake Bala, an obvious visual reference, and Cadair Idris) you head towards Cadair and look for the V shaped entry to the left of that mountain. If you are leaving the pattern you continue straight ahead over the Tal-y-Llyn lake towards Tywyn, however if you are going around for another run you should position yourself to the right side of the valley ready for a sharp turn just before the lake ('Corris Corner'). If you've positioned yourself correctly, it's between 90 and 100 degrees - too fast or a lazy turn will see you in the hillside. Follow the valley down to just north of Machynlleth, then turn to follow the Dyfi Valley north easterly until you reach Dinas-Mawddwy - turn just before there and drop over the top back into the circuit.
If you have google earth installed, have a look before you fly it. There are quite a few valleys around there and it's easy to follow the wrong one and find yourself with no exit if you've not planned it.