Including Diffwys Dwr and Pistyll Gwyn - Afon Las.
From Cardiff, take the A470 to Betws-y-Coed. From Betws-y-Coed, take the A5 towards Bangor. Follow the road to the far end of the lengthy village of Capel Curig, then turn left onto the A4068, signposted to Caernarfon. After passing the lakes, turn right by the Pen y Gwryd Hotel to remain on the A4086. It climbs to the high point at Pen-y-Pass - the head of Nant Peris - where there is parking space if needed (it fills up very quickly, as this is the start of many Snowdon routes). Continue past Pen-y-Pass, and park if possible in the first lay-by on the left - this also fills up very quickly. SH 6284 5668.
This walk is entirely on-road, as there are no proper paths in the valley (the mountains are all open access wilderness, so paths are not needed), and this does mean that it is possible to drive the entire route - this is often how these waterfalls are seen, while on the way to one of the other waterfall sites further along in the valley. If walking, be warned that this is a very busy and very popular road, and you will share it with numerous vehicles. If you can cope with walking without paths, you are best off walking along the slopes above the right side of the road.
Walk downhill along the road. The first large valley on the left, Cwm Glas Mawr, has numerous little waterfalls (and various paths used by climbers to reach the crags). One of the large crags on the left about half way up the valley contains Diffwys Dwr. In most conditions, it just looks like a 61 metre black smudge down the cliff, but in winter it can freeze into a spectacular ice display.
Continue down the valley until you reach some houses on the right. High on the crags above them is Pistyll Gwyn. Return using the same route, or walk further down the road to the Nant Peris parking area, where there is a bus service up to Pen-y-Pass.
If you want to extend the route, there are possibilities, but I have not followed or graded these extensions. For getting closer to Diffwys Dwr; at the first track on the left from the lay-by, cross the track's bridge, continue ahead over a stile, cross a footbridge, then head left along the stream bank, as far as you want to go up the valley. For getting closer to Pistyll Gwyn; just after it comes into view, there is an alcove on the right side of the road with a postbox and three gates. Go through the middle gate and follow the track until it dies. Continue upwards through fields towards the tree-lined stream, to locate another path running along its right bank. Follow it upwards around several rocky outcrops, to reach the waterfall (or even continue onwards to the Devil's Kitchen).
Whilst every care has been taken in the compilation of this description, neither the author nor his fellow walkers can accept responsibility for loss or injury arising from any errors, omissions or inaccuracies in this description. This description is intended as a guide only, and you should select a route to suit your own abilities, at your own discretion. Ability requirements are a guide only. You follow this description at your own risk.