Stunning scenery coupled with a steep climb of a one in 40 gradient means the track uses huge horseshoe curves, doubling back on itself nearly to gain 400f (121m) over four miles (6km).
The opening of the latest stretch of track has predictably been welcome by some but not by others.
A handful of protesters were track-side near Beddgelert with placards proclaiming their unhappiness at the track cutting through their land.
The first train on Tuesday - with local dignitaries- was delayed after vandals put an iron bar into one of the signals, and someone broke into a building at Rhyd-ddu station.
One of the lawful protesters, Eira Taylor, condemned anyone acting illegally and said the campaign group would never do anything which might put anyone at risk of injury.
"We've always maintained a peaceful protest, and we would not vandalise anything," she said.
I'm so looking forward to this trip
John Pritchard, 93-year-old from Beddgelert
General manager Paul Lewin said he had "every respect for protesters who wanted to make their point" and there was "no excuse for vandalism".
He was however very happy that the day had arrived when a passenger-carrying train had made it to Beddgelert - after 32 test runs.
The railway company prides itself on creating jobs locally.
Andrew Williamson works as a fitter: "I see it (extending the line) as guaranteeing our jobs.
"It's a fantastic thing for the area, which will bring in lots of money," he added.
It has taken the last six years to lay the track, and the section from Beddgelert to Porthmadog will not open this year, due to a dispute over money for work done on one of the bridges.
John Prideaux, chairman of the Ffestiniog Railway Trust said it was "disappointing" that the whole track would not open.
There are plenty of photo opportunities on the run
But added that, looking at the big picture, it was just one of those things which comes from such a large project.
Mr Prideaux should know about big projects, as he was one of the people responsible for the channel tunnel.
Although far smaller in scale than the chunnel the fact the Welsh Highland is run by a charitable trust makes the £28m project to link Caernarfon to Porthmadog pretty huge, he said.
It provides job opportunities and brings the area alive, he said.
"This is not dead heritage," he added.
Volunteers on the line are sometimes perceived as people from outside the area, but Elwyn Jones was on the train with a group of local people who either volunteered, or did work on the line.
"This is a fantastic event. We've been waiting for years for this, but it has been worth it," he said.
"The project has hit a lot of brick walls on the way but we've come through them all."
Mr Jones dismissed claims that the train would not bring benefit to the area.
"People coming here on holiday will have time to travel on it and enjoy the area, and local contractors work on the line," he added.
Not everyone is convinced.
Jacky Fell, with the group Gwarchod Beddgelert (Protect Beddgelert) had staged a track-side protest with a model of a white elephant.
Speaking before the event she said she was "sad" the train was cutting through and "ruining" the countryside.
"It is an over intrusive hobby", she said.
Others from Beddgelert took advantage of the train company's offer for tickets to travel on the line from the village to Rhyd-ddu.
Among them 93-year-old John Pritchard, who remembers the train in the village during his childhood.
Mr Pritchard had over-come a heart-attack at Christmas, and seven weeks in hospital, to make it as a VIP guest.
"I used to run from school to catch the train to go to my grand-mother's house," he said.
"I'm so looking forward to this trip," he added.
Time will tell whether the train will really benefit the area.
Gwynedd councillor Alwyn Gruffydd called it "a historical day", but added he remained to be convinced that visitors would let the train take the strain by keeping cars out of the area.
Whilst another local councillor Selwyn Griffith added: "We must make the best of it."
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