The pass of the cold door
Bwlch Oerddrws — roughly, the pass of the cold door, and a name the weather earns regularly — carries the A470 over the eastern shoulder of the Waun-oer ridge between Cross Foxes and Dinas Mawddwy. It is the odd one out among the drives here: a genuine mountain crossing on a two-way trunk road, with a white line down the middle and no single-track sections. That makes it the pass to take when the weather is poor, the vehicle is large, or nobody fancies reversing on a gradient.
From the Dolgellau side the road leaves the A487 at Cross Foxes and climbs east; from the Machynlleth side it is the A470 up through Cemmaes and Mallwyd, past Dinas Mawddwy — about ten miles from town — and then steeply up the head of Cwm Cerist to the summit.
How high is it? An honest answer
We could not settle this from a primary source, and would rather say so than invent a figure. Oxfordshire County Council's heritage photograph archive catalogues an image of the pass as “the 1200 foot high mountain pass on the A470 road from Dinas-Mawddwy to Dolgellau”, which puts it somewhere around 360 metres — but a photograph caption is not the Ordnance Survey, and it is not a highways document either.
What can be said with confidence is that the summit sits well below Bwlch y Groes, a few miles east, generally given as 545 metres; that the ridge north-west of the pass rises to Waun-oer at about 670 metres; and that the road is high and exposed enough to be closed by snow while the valleys either side are clear. If you have an OS Explorer sheet in the car, the spot height by the road is the figure to trust.
What the climb is like to drive
This is a proper mountain gradient on a road built for lorries, a different proposition from a mountain lane. Going east from Cross Foxes the ascent is steady; going west from Dinas Mawddwy the road pitches up sharply at the head of Cwm Cerist and climbs through bends that tighten as they gain height. Heavy vehicles slow to a crawl on both sides, and the sensible thing is to sit behind them: on a pass with crests and bends, the safe places to pass are far fewer than they look.
Weather is the real variable. The summit collects cloud and wind: a crosswind here catches high-sided vehicles, caravans, motorcycles and cyclists hard, and the gusting is worse at the top than anywhere else on the crossing. Snow, ice and drifting are all normal in winter. The A470 is a trunk road maintained by the North and Mid Wales Trunk Road Agent and appears on the Traffic Wales alerts feed — check it rather than guessing, because when this pass shuts the diversion is a long way round.
The laybys, and the Mach Loop question
There is no car park at Bwlch Oerddrws, only laybys on the A470 at and near the summit, and they are the only places to stop on the crossing. They are also, on any promising weekday in the flying season, full — because the hillside above the pass is what the specialist guides call the most visited viewpoint on the Mach Loop, the military low-flying route through LFA7, and aviation photographers arrive early to walk up it.
That is a different day out, and it has its own page: see Bwlch Oerddrws on the Mach Loop for the walk up to the ledges and the honest odds of seeing anything. If you are here for the drive rather than the aircraft, the practical consequence is that you may not get a space. Move on to Cross Foxes or Dinas Mawddwy rather than improvising: parking half on the carriageway of a trunk road, on a gradient, where approaching traffic cannot see you, is genuinely dangerous.
The Red Bandits of Mawddwy
This pass has a reputation older than the road. Visit Mid Wales describes it as the country of the Red Bandits of Mawddwy — the Gwylliaid Cochion Mawddwy — sixteenth-century robbers known for holding up travellers crossing Bwlch Oerddrws at the upper end of Cwm Cerist. The place names remember them: Llety'r Lladron, the robbers' lodging, and Llety'r Gwylliaid, the bandits' lodging.
The story carries over the ridge. Near Bwlch Llyn Bach, on the far side of the Waun-oer ridge above the Tal-y-llyn pass, a rock called Llam y Lladron, the robbers' leap, is where the bandits were said to have been thrown to their deaths. Two passes, one gang, and names that make more sense once you have seen how narrow the ground is.
Walking and stopping either side
The pass is a walkers' starting point as well as a driver's. The ridge north-west of the summit carries the Waun-oer and Maesglase tops — rough, wet mountain ground rather than a path in the ordinary sense. Visit Mid Wales gives its Waen-oer ridge route as a nine-mile, six-hour circuit from the car park in Dinas Mawddwy at grid reference SH 859 149, a more sensible place to leave a car than the summit laybys.
At the western end, Cross Foxes sits on the A470–A487 junction at the foot of Cadair Idris, where there is a bar and grill with rooms; Dolgellau is a few minutes further on. At the eastern end, Meirion Mill at Dinas Mawddwy is signed off the A470 and has a shop and coffee shop with level access, plenty of parking and a disabled toilet, listing opening daily from 10am to 4pm. Cwm Cywarch, the dead-end valley under Aran Fawddwy, turns off nearby.
Practical information
The crossing is short, so this is a pass to combine with something else. The obvious pairing is a circuit: north over Bwlch Llyn Bach and the Tal-y-llyn pass to Cross Foxes, east over Bwlch Oerddrws, and back down the A470 to Machynlleth, which takes in two passes and a lake in one loop. The more ambitious version adds Bwlch y Groes from Dinas Mawddwy, a full day and a different order of road.
Fuel is available in Machynlleth and Dolgellau but not on the pass. There is no toilet, no shop and no shelter at the summit, and mobile signal on the tops is patchy. The TrawsCymru T2 does not cross this pass; route 36 links Machynlleth with Dinas Mawddwy via Cemmaes, so the eastern foot is reachable by bus — see getting around. Check the forecast and Traffic Wales alerts in winter, and see our practical driving guide for more.
Day trips