Narrow-gauge railways in Russia
The Imperial Russian narrow railway track gauge was 3 ft 6 in (1,067 mm), the current track gauge is predominantly 750 mm (2 ft 5+1⁄2 in). In Soviet Russia, narrow-gauge railways were mostly common in forestry and peat industries in low inhabited places.
Source: Wikipedia — Narrow-gauge railways in Russia (CC BY-SA 4.0)