In 1904 a loop line of the Trans-Siberian Railway was built around which obstacle?

On the 17th of March 1891 Czar Alexander III signed a rescript for building the Great Siberian railway. The Trans-Siberian Committee was formed to control the process of the construction. The plan based on the proposals of S.U.Vitte, the Minister of Finance. However, strict terms were laid down. The Great Siberian railway had to be built only by Russians and with Russian equipment.

In 1900 the line from Moscow to Vladivostok became operational. But there was no railway to bridge the gap between the middle Siberia and the Trans-Siberian railways. So, until 1904 passengers crossed Lake Baikal on ferries.

The Trans-Siberian Committee realized that however expensive it might prove The Circum Baikal Loop (Circumbaikal / Roundbaikal Railway) had to be built. In 1901 10,000 laborers started to work on the line. It was the most difficult to build on the rocky terrain. Working as fast as possible and in all weathers. The Circum Baikal Loop was completed in 1904 at a cost of 70 million rubles.