The first public railway in Russia was the Tsarskoye Selo Railway which ran a modest 27 km from Saint Petersburg to Pavlovsk. It opened in 1837 using a mixture of steam locomotives built in England (Stephenson 'Patentee' class) and Belgium. See the Wikipedia article.
The sheer size of the Russian Empire meant that travel from the centres of power in Moscow and St. Petersburg to remote lands like Siberia was difficult and time-consuming in the 19th century. The construction of railways to link these remote areas seemed essential and, in 1891, work on the 9,000 km long Trans-Siberian Railway linking Moscow and Vladivostok was authorised by Tsar Alexander III. The heir to the throne, Nikolai Alexandrovich, inaugurated the project in Vladivostok and building proceeded simultaneously at both ends of the line. Over 66,000 men were employed on the herculanean task.
In 1898 the first train arrived in Irkutsk, having travelled around 5,000 km from Moscow. However, beyond Irkutsk, the area around Lake Baikal presented a problem. One possible route from Irkutsk to the southern side of Lake Baikal and the line to Vladivostok would require a climbing route averaging a gradient of 1 in 75 for 30 km. This was regarded as beyond the capabilities of the available locomotives. The second possible route followed the west bank of the Angara River upsteam to the Lake, then continued south west, hugging the shoreline of Lake Baikal to reach the southern side of Lake Baikal and the line to Vladivostok.
The second of these routes, called the 'Circum-Baikal Railway' was adopted. The line from Irkutsk to the Lake near the village of Baikal was completed without much difficulty but the 90 km of construction along the shoreline of the Lake caused significant delays because of the large number of tunnels, galleries and bridges required. In order to commence through services, it was decided to bring trains from Irkutsk to the temporary terminus at Baikal and use ferries to tranship passengers and cargo to the southern shore of the Lake at Mysovaya.
Two icebreaking ferries were ordered from Armstrong Whitworth in England. They arrived part-built and were commissioned in Russia. The first, 'Baikal', was a train ferry, that is to say passenger and freight cars could be run onto special tracks on her deck and transported intact across the Lake to the other section of the Trans-Siberian Railway.
The second ferry, 'Angara', was a passenger and cargo ferry without the facility for carrying railway wagons. To accommodate these vessels, special docks were built, largely in wood, on either side of the Lake at Baikal (which became Port Baikal) on the northern shore and Mysovaya (now called Tankhoy) on the southern shore. These services commenced in 1900.
Lake Baikal is almost 400 miles long, up to 50 miles wide, prone to sudden storms and freezing in winter so the ferries were no soft option. Both ships had specially-shaped hulls which could bear down on ice and crack it, allowing the ship through. When the ice became too thick for the ferries, the expedient of laying a temporary railway track across the ice was tried but with only limited success. At least one locomotive is supposed to have disappeared through the ice.
Meanwhile, construction of the first track of the Circum-Baikal Railway forged ahead. Originally scheduled for completion in 1905, the railway was operational by September 1904 because of the Japanese threats which preceded the Russo-Japanese War of 1905. Completion of 'the Golden Buckle of the Russian Steel Belt' (as the Circum-Baikal Railway has been poetically described) gave an important advantage in moving men and materiel. To increase the capacity of the railway, work continued on adding a second track which was brought into service in October 1915.
Once the Circum-Baikal Railway was complete, the ferries were withdrawn. However, 'Angara' made a new career as a general ferry criss-crossing between the various small ports around the Lake, surviving long enough to be taken into preservation.
Between 1947 to 1949 a new railway was built broadly on the climbing route between Irkusk and the southern side of Lake Baikal which was originally rejected. Much more powerful locomotives were available and the new line is electrified at 25 kV a.c. and now carries all the through traffic on the East Siberian Railway section of the Trans-Siberian route.
Another project in 1956 provided hydro-electric power to the Irkutsk region by damming the Angara River between Lake Baikal and Irkutsk. This resulted in the original railway line between Irkutsk and Port Baikal being flooded, breaking the original 'Golden Buckle'. The remaining part of the Circum-Baikal Railway from Port Baikal to the southern side of Lake Baikal has been singled and retained, providing a spectacular tourist route.
'The Circum-Baikal Railway: A Concise Guide Book (3rd edition)' by A.K. Chertilov translated Ye. Luganskaya (Artizdat, Irkutsk) ISBN 978-5-93765-044-3.