I believe its the term used to describe the Elan Valley road towards Cwmystwyth, Devils Bridge Aberystwyth road.
A mobile signal is virtually non existent in this very remote area of Mid Wales, there is no significant population to justify the installation of radio masts.
You can also pick up the Abergwesyn Common road from this terribly remote circuit.
The rainfall in this remote area is some of the highest in Wales, almost to rival Capel Curig, and this is why so many reservoirs were sighted in this area of Wales.
In total, there are around fifteen separate reservoirs, including the main Elan Valley ones.