Novosibirsk

Novosibirsk was a city in Siberia. The city had underground tunnels built to serve its residents.

The city was the site of a UNIT base. (TV: The End of Time)

Alternate timeline
In one possible timeline, extreme climate change and nuclear war on Earth led to the city's destruction, leaving it in ruins, with the planet becoming known as Orphan 55. Tranquility Spa was built a short distance from the ruined city.

The city's tunnels were explored by the Thirteenth Doctor and Team TARDIS following the Dregs' attack on Tranquility Spa. (TV: Orphan 55)