But while the scenery may be spectacular, one Glasgow councillor says ScotRail's trains on the famous West Highland Line are "letting Scotland down."
Passengers say the service is not getting the investment it needs, despite attracting swathes of tourists each year.
Complaints include frequent breakdowns, heating problems during the height of winter and poor quality trains.
Passengers travelling from Fort William to Glasgow on one of last week's early morning services had no access to a toilet on the four-hour journey because both were broken.
Regular passengers say they are often advised to move to a warmer coach by ticket staff.
Now Glasgow SNP councillor Graeme Hendry is to raise the issue with Scottish Transport Minister Keith Brown.
Mr Hendry said: "This route is one of the best journeys in the world and the service should reflect that.
"ScotRail is letting Scotland down by providing a poor quality of service.
"We all understand money is tight but to have no toilet or heating facilities is unacceptable.
"Given this is Glasgow's gateway to the Highlands I will ask the Transport Minister to raise it with ScotRail."
The criticism comes despite passenger numbers rising 14% over the past three years.
The route has always been popular but films such as the Harry Potter series and Skyfall, the latest James Bond movie, have boosted its popularity.
The line from Glasgow to Mallaig is 164 miles long and runs by Loch Long, Loch Lomond and Loch Eil. Return tickets cost about £50.
It crosses the world's first concrete rail viaduct at Glenfinnan, which was featured in the Harry Potter films.
The West Highland Line was voted the World's Greatest Rail Journey in 2010 by readers of independent travel magazine Wanderlust for the second time, beating such famous trips as the Trans-Siberian in Russia and the Cusco-Machu Picchu line in Peru.
But there has been fierce criticism of the trains used on the Scots line.
One regular passenger, a 69-year-old former British Rail employee, from Ayrshire, said: "The rolling stock on this route is more than 30 years old and not fit for a journey of 3½hours.
"This line has been forgotten. Standards have not only slipped, but have crashed. The trains were better 40 years ago. You had compartments and passengers could get a hot meal.
"There is no reason why this service should not have a first class section and a buffet car.
"Spare a thought for the poor employees who have to tell passengers the toilet is not working again or to move to a warmer coach."
Another passenger said: "Despite the summer months being packed, ScotRail uses an older, slower, and sometimes quite uncomfortable train for this service. It grates that it does not even bother with the buffet car."
Tourists said they had also been left baffled by the station information displayed electronically on trains.
The train from Glasgow splits at Crianlarich, with one half going to Oban and the other to Mallaig. But the train only displays stations to Oban until it reaches Crianlarich.
However, ScotRail defended its service and the state of the trains. A spokesman said: "Clearly, we are doing something right as the West Highland Line has been voted the World's Greatest Rail Journey in recent years – and the routes have also seen a 14% increase in passenger journeys in the last three years.
"Since taking over the franchise in 2004, we have carried out substantial refurbishments of our Class 156 trains. In the last 12 months, we have upgraded the trains' toilets, heating systems, seats and interior doors to further improve comfort for our customers.
"As is right and proper, we will respond directly to customers should a complaint be made."