Vladivostok was a port city located on the Pacific coast in Russia, a nation on Earth.
The Fifth Doctor, Tegan Jovanka and Turlough visited St Petersburg in 1904. Due to a teleportation accident, Tegan and Turlough were transported to Vladivostok, where they were forced to take a train back to St Petersburg. (PROSE: Gudok [+]Error: Code 2 - no data stored in variables, cache or SMW.)
Prior to the 1930s, the Russians began constructing a railway between Vladivostok and European Russia. This threatened the Chinese region of Manchuria with trade strangulation and influenced Japan's decision to invade in 1931. (PROSE: The Shadow of Weng-Chiang [+]David A. McIntee, Virgin Missing Adventures (Virgin Books, 1996).)