Reading old copies of The Railway Magazine has been an enjoyable pastime over Christmas (2018). In the June 1950 issue of the magazine there was an article about travelling to the Sognefjord by rail.
The railway from Bergen to Voss was projected as the first part of a through route from the West coast to Oslo. The line from Bergen to Voss was completed in 1883 but it was not until 1894 that the remainder of the line was authorised. Ultimately the shortest route for the line was chosen even in the knowledge that this would involve the longest and highest mountain crossing.
To overcome the difficulty of transporting men and materials to the construction camps in the mountains, many miles of road were constructed. One if the most remarkable of these was constructed from Flam at the head of the Aurlandfjord, to the railway at Myrdal, a distance of about 10 miles.
Before the mainline from Bergen to Oslo was completed, it was proposed to supercede this steep and winding road by a railway from Myrdal to Flam. The rise to Myrdal was 2,800 ft., the majority of which occurred in the short length at the head of the valley. Exceptionally severe gradients were unavoidable. It was obvious that, if the railway was to be operated by adhesion, it would be necessary to increase the length of the line by a spiral. The idea was, as a result, shelved for a number of years.
The railway was authorised in 1924, and construction began almost at once,
with the boring of Vatnahalsen Tunnel, near Myrdal. This remarkable tunnel is 1,000 yd, long, and describes a reverse curve of 7.5 ch. radius in the mountainside, on a gradient of 1 in 19. The upper portal is 132 ft. above the lower. About 700 yd. of the bore were driven from the
lower level. Only a small staff was employed, and ten years were occupied in the construction of the tunnel. The headings driven from each end met on 15th May 1934, with only a negligible error Altogether there are 20 tunnels on the line, with an aggregate length of over 3.5 miles. Quite apart from the tunnels, a considerable portion of the railway at the head of the valley is protected by snow-sheds.
The construction of the railway was completed in 1942, at a cost of more than £1.25 million, but the wartime shortage of rolling stock delayed the opening of the line, and regular traffic did not begin until 24th November 1944. The main line from Bergen to Oslo is steam-operated (1950), but the branch to Flam is electrified on the overhead principle. The track conforms to standard Norwegian main-line practice, and is laid with flat-bottomed rails weighing 72-lb per yard. It is heavily ballasted and well-maintained. The railway is single throughout, and is worked on a train despatching system, without fixed signals.
Reading through the article in The Railway Magazine, I was struck most forceably by the maps showing the line, and most particularly by the maps which show the spiral arrangement of the line close to Myrdal. The relevant sketch map in the magazine is reproduced below.The Flam Railway. 
More information about the line is available on-line. Visit https://www.visitflam.com/flamsbana, for up-to-date information, and https://www.visitflam.com/editorial-content/the-history-of-the-flam-railway, for more on the history of the line.
1. By Rail to the Sognefjord; The Railway Magazine, Volume 96, No. 590, June 1950, p406-409.
2. The Railway Magazine, Volume 96, No. 590, June 1950, p407.
3. The Railway Magazine, Volume 96, No. 590, June 1950, p396-397.