This is a tale of two steam trains. You thought it was the story of climbing a mountain, and it’s that too; but this is a mountain like no other in Britain, and the trains have a lot to do with it. Even if you don’t ride them, they’re part of the backdrop, parts of the sights and sounds and smells that make this mountain one of a kind.

This mountain is, of course, Snowdon (never Mount Snowdon, please); its Welsh name is Yr Wyddfa. As the highest peak in Wales (and England too), it’s got a lot more going for it than just the trains. And it’s not just the highest, but one of the best; there are many who’d say it’s the best.

Snowdon is more than just a mountain. From its peak–and it’s a properly peaky peak–three main ridges descend; but each of those ridges divides again lower down, creating a complex of lower peaks, subsidiary ridges, cwms and crags. So, though I’ve been to the top a dozen times, and climbed on the lower slopes many times more than that, it’s not really surprising that I can find ways up that I’ve never used before.

Today I’m climbing from Rhyd-Ddu, on the relatively unfashionable south-west side of the mountain. Ten minutes in, striding a wide gritty path that climbs gently past boulders and twisted thorn trees. Stocky black cows watch me placidly; a kestrel hovers above, pinned to the sky by its own rapt gaze, but I cannot see another human.

In the valley just below me, however, a little steam-train huffs and hoots. Rhyd-Ddu is a stop on the Welsh Highland Railway which currently operates from Caernarfon, through Beddgelert to a terminus at Pont Croesor; Rhyd-Ddu is about the halfway mark. Soon, all being well, the service will extend all the way through to Porthmadog; the track has been laid but supporting work, like the installation of signals, remains. Regular services are expected to begin in 2011.

I’m feeling as if I’ve missed something in not arriving by train, but the railway is only part of the Snowdon transport jigsaw. Even more valuable to walkers and climbers are the Snowdon Sherpa buses. It’s the buses that have brought me effortlessly from breakfast in Llanberis, via Pen-y-Pass and Beddgelert, to Rhyd-ddu. It’s thanks to the buses that I can tackle Snowdon in the best possible way: up one side and down the other.

Walkers can choose from six main routes up Snowdon: working clockwise  from the north, these are the Llanberis Path, Pyg Track, Miners’ Track, Watkin Path, Rhyd-Ddu Path and Snowdon Ranger Path. And, rather wonderfully, all of them are accessible by Sherpa bus. By my calculation, this makes for 60 different possible combinations of ascent and descent. That should keep me going for a bit...

This mental arithmetic fortunately coincides with an easy bit of path. Of course it can’t last; this is a mountain, after all. The gradient kicks up, the path gets rockier and in places I’m sharing it with a small stream. I pace steadily upwards, the path curling across a wide hillside, climbing towards the clouds. Suddenly it’s not a broad hillside any more; there’s nothing on my left but grey rocks slithering into the mist. This is Llechog, not one of Snowdon’s renowned climbing crags, yet it looks steep and bare enough to me. 

The path is shepherded up some zigzags by wire fences, then suddenly I’m on a narrow ridge, with drops both sides. To add to the drama, the clouds are shredding and big views suddenly appearing. It’s an impressive place; not as exposed as Snowdon’s more famous ridge, Crib Goch, but hardly somewhere you’d saunter along with hands in pockets.

As the narrow ridge blurs into a broader slope, I know I’m near the summit. If I needed confirmation, the bass panting of a steam engine just over the skyline settles it. Another minute or two brings me to Hafod Eryri, the new summit station and café which opened in 2009. It’s a vast improvement on the ugly blockhouse which stood here since 1935, though it must be said there are still many who feel mountain summits shouldn’t be desecrated by cafés, or steam trains, or in some cases anything at all. It’s a fine argument, but in this case it’s academic. Hafod Eryri’s here to stay, and the trains have been puffing up Snowdon since 1896. And, of any mountain in England or Wales, Snowdon can take it.

It’s just a minute more up to the summit. The new building isn’t hidden from here but it doesn’t obstruct what is unquestionably one of the best mountain views in Britain. Today, as the clouds scatter, I feel I can see most of Wales. A shadow on the sea far to the north may just be the Isle of Man. Today, however, I’m not blessed with the exceptional visibility which can bring both the Lake District fells and Ireland’s Wicklow mountains into view.

With a view like this, the café loses out to flapjack and water on the summit itself. I pick out peaks and contemplate future routes. The Sherpa buses don't just serve Snowdon, after all. They open up loads of other possibilities, like the Glyderau, the next great ridge to the north, beyond the gulf of the Llanberis Pass. A complete traverse, from Capel Curig to Bethesda or vice versa, would be 20km, and the other possible permutations multiply beyond easy reckoning.

And even today, right now, as I lick the last crumbs from my fingers, I have choices to make. I started with a plan but plans can change, especially as I’m not restricted by having to return to a parked car. The buses mean that Snowdon is my oyster.

In the end, I stick to plan A and descend the Llanberis Path. As the longest of those six main paths, it can seem a bit of a grind coming up, but it does have a relatively gentle gradient most of the way, which makes it a fast and easy way down. It runs roughly parallel to the railway at first, across a broad hillside and then skirts above a steep slope plunging craggily to the Llanberis Pass. Then it ducks under the railway and slips away down the hill.

As I stride down here I keep glancing over my shoulder to the great crags of Clogwyn du’r Arddu, locked in shadow under the ridge of the Snowdon Ranger path. Climbers call it ‘Cloggy’, but they do so with respect. Leo Houlding, one of today’s top all-round mountaineers, has called it “the best crag in the world”.

The next landmark is the little café at Halfway House, but I’m into my stride and keep on going, ducking under the railway again as another train comes bustling up in a flurry of steam and smoke. The path meets a lane and I let gravity pull me down the last incline before turning left, under the railway one last time, past the church and into the outskirts of Llanberis. Soon I’m sipping tea from a pint mug, waiting for a bowl of chilli, and thinking about the next time.