IT has twice been voted the world's greatest train journey.
However, a Glasgow councillor has said ScotRail's West Highland Line trains 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 in winter and ageing trains.
Passengers travelling from Fort William to Glasgow on a recent service had no access to a toilet on the almost four-hour journey as both were broken.
ScotRail says it has it had carried out substantial investment in the trains but said it had to balance the needs of rail travellers across Scotland. However, Glasgow SNP councillor Graeme Hendry is to raise the issue with Scottish Transport Minister Keith Brown.
Mr Hendry said: "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."
One regular passenger, a 69-year-old former British Rail employee, from Ayrshire, said: "Standards have not only slipped, but have crashed. The trains were better 40 years ago."
A ScotRail spokesman said: "We are doing something right as the West Highland Line has been voted the world's greatest rail journey in recent years and there has been a 14% increase in passenger journeys in the last three years."