|Length:||9.9 miles (15.9 km)|
|Route outline (key)|
The B4405 is a rural B-road in south Merionethshire.
The road starts deep in the Welsh mountains at Minffordd on the A487. Although overlooked by such heights as Cadair Idris and Graig Goch it remains firmly in the valleys. It heads southwest, vaguely parallel to the A487 for about half a mile, before reaching a steep, narrow road connecting it back to the A487. The road is no-entry from the B4405 end (and signed as unsuitable for motors from the A487 end) so it is not surprising that the B4405 follows the route it does.
The road quickly reaches the shore of Tal-y-llyn Lake and follows it to the village of that name at the other end. It then continues along the valley. For many people, Tal-y-llyn refers to a narrow-gauge railway; this does go along this valley but never reached its namesake. The B4405 has to continue for another couple of miles and go through the village of Abergynolwyn before the Tal-y-llyn Railway is reaches. The road then follows the line closely for the rest of its length, although it is rarely visible from the road.
The River Dysynni, which the B4405 had been following from the beginning, moved away at Abergynolwyn and so the valley the road is in narrows considerably from then on. The next hamlet is Dolgoch, famous for its waterfalls (which are invisible from the B4405), after which the valley begins to widen out. The B4405 hugs the northern edge and the railway line the southern.
Eventually the B4405 reaches the village of Bryncrug, close to the point where the two valleys it has travelled through join. It skirts the edge of the village before ending at a T-junction on the A483.