In reply to planetmarshall:
1 - Snowdon loop -Its a great run on 'trail' surface with a good amount of climbing and great views, plus you can impress all the walkers by running down! Its about 15k
From Llanberis head up past the YHA to a place marked on OS map as Burnt Mound and Brithdir. The road turns in to a nice track. Follow this along and up to the pass between Foel Goch and Moel Cynghorion, then descend along grass to a trail junction. Here turn Left along the Ranger path which zig zags up to the summit of snowdon. Turn around then descend along the Llanberis path.
2 - Llanberis loop - low altitude trail / road
Head out of the village towards pen y pass and turn left before the Hotel / opposite the Snowdon train station. Follow the footpath to the Slate museum then turn left through the car park and continue on up to the old quarry hospital. Continue left along the path now through the trees alongside the lake gradually heading up but bearing left at junctions.
Either way you go youll get to a small road. Here you have two options, head left down Fachwen to the end of the lake. follow the road around and back towards Llanberis, you can then pick up the lake trail and run back which is a pleasant loop.
Or when you reach the small road you can turn right and head uphill for a short while untill you get to a T junction, turn Right here and follow the road to its terminus at Deiniolen quarry. Here the trail continues along a slate trail before Zigzagging down with good views back to Llanberis and castell Dolbadarn. Turn Right on the road to head back to the village.
3. Carneddau loop (best to have an OS map for this route) - mix of fell and trail
Start – from capel curig direction travel towards Bethesda/Bangor on the A5 then park on the left just after Gwern Gof farm before you get to lake Ogwen.
Cross the road over a bridge to a small group of trees and continue on the farm track to a stile and on to the mountainside. Follow the vague path up through wet ground, marked with wooden posts, the target is a stile further up on the mountain wall.
Continue up this path along the river until a lake is visible at the top, here the path bears left up the rocky path to the top of Pen yr Ole Wen. The trail flattens out quickly and descends to the plateau leading to Carnedd Dafydd.
Continue along the path to Carnedd Llewelyn, here are great views in all directions. Behind the summit shelter / cairn there is a path leading steeply down, this flattens out then some fun scrambling, then turn right down towards the lake below and follow the track beyond.
Once you get to the road head right for a short while then turn first left to gain a wide track. Continue right along this back to the Start.
Here are links to GPX files
https://onedrive.live.com/redir?resid=8972EB6A1CB6CB97!1481&authkey=!AL0Qck...
Post edited at 20:24