Views of tunnels and stations of Sokolnicheskaya and Koltsevaya lines of Moscow Metro from drivers cabin of track measuring train «Synergy-1» (model 81-717/714). More information about train: \r<br>\r<br>Attribution:\r<br>By Alexander Popov aka Russos ( [CC BY 3.0 ( via Wikimedia Commons.\r<br>Source:
