As the diesel engines growl up the bank through leafy Helensburgh, you see ships riding at anchor in the estuary before they disappear behind woods of birch and oak above Gare Loch.
From Garelochhead there is a spectacular view back along the narrow loch to the south.
Later, the views along Loch Lomond are some of the finest on the journey, the railway running along a shelf cut into the hillside above a dense canopy of trees. A summer ferry links Inveruglas with the idyllically situated Inversnaid Hotel on the opposite shore. The long climb up Glen Falloch beside the birch-fringed river ends at the junction for Oban at Crianlarich and the meeting of three glens.
Once the railway has passed the end of Loch Tulla, it is 51km before anything more than a track is seen again. The wilderness of Rannoch Moor is majestic, one of those rare places in Britain where little has upset the course of nature. The pause at Rannoch station usually sees a few well-equipped walkers alight, enough to support a tea-room in summer and the adjacent Moor of Rannoch Hotel. The shed covering the line at Cruach, north of Rannoch station, was built to protect the track from drifting snow and is unique in Britain.
The people who got to know this isolation best were the few railway staff at Corrour, the highest station on the British rail network at 408m, where an old railway carriage on the platform once served as a school attended by 11 children. Today the only residents occupy the Swedish-designed Corrour Station House Restaurant with rooms built beside the railway in 2000. Here you can dine on venison from the 21,000ha Corrour Estate and sup Cairngorm Brewery ales.
The treeless, undulating peat bog continues, with lonely Loch Treig below the line to the west, until Tulloch station, where the road from Kingussie joins the railway to reach Fort William. But one more spectacle is in the Monessie Gorge, where the river is squeezed into a frothing cataract.
The panorama of mountains, dotted with sheep pounds and poignant remains of crofters' cottages, is soon complemented to the west by views over sea lochs towards the isles of Muck, Eigg and Rum. The brilliant blue sea, edged with translucent emerald-green, reminds some of the South Seas, an impression that is encouraged by the sight of palms and subtropical plants growing under the benign influence of the Gulf Stream.
Beyond Lochailort station, you see a small white church on a knoll: the deconsecrated Our Lady of the Braes. It was on Loch nan Uamh, the Loch of the Caves, that a hopeful Charles Edward Stuart landed from a French frigate in 1745, only to leave from the same spot 14 months later after the disaster of Culloden. Past Arisaig, Britain's most westerly station, the railway cuts across the western end of Loch Morar which, at 310m, is Europe's deepest lake. On autumn nights, thousands of eels swim out of this loch on an extraordinary 4800km journey to the Sargasso Sea to lay their eggs.
Running beside beaches of white quartzite sand sometimes populated by sauntering cattle, the train slows for journey's end at Mallaig station, adjacent to the fishing and ferry harbour. The railway's history is one of many subjects explored in the nearby Heritage Centre.
Moments
Perhaps the most impressive moment on the way to Fort William comes just north of Tyndrum station, where the railway describes a horseshoe curve beneath the immense Fujiyama-like shape of Ben Doran while crossing two curved viaducts.
On the Mallaig line the highlight is undoubtedly the northbound climb to Glenfinnan station across the famous viaduct, set in an amphitheatre of mountains and overlooking the Glenfinnan Monument, erected in 1815 in honour of Bonnie Prince Charlie raising his standard in 1745.
Tips
A catering trolley is available on some trains. The Caledonian Sleeper includes a lounge car serving snacks and drinks. Reservations are required for bikes. Compartments are comfortable and equipped with a basin, and beds made up with linen.
CHECKLIST
Details: Trains are operated by ScotRail.
Since 1984, steam-hauled trains have been a regular feature of the Fort William-Mallaig line, today in the form of the Jacobite, a morning weekday train. It runs between May 13 and October 25 and at weekends from June 22 to September 22.
What to pack: An Ordnance Survey map to identify the lochs and mountains. If walking from a station in midge season, mosquito repellent. You'll need ear plugs on the Caledonian Sleeper.
