Felwinter called on Castor to negotiate, but ended up killing Castor's Ghost and pushing him off the mountain. On the run from Rasputin's Warsats and combat frames, Felwinter and his Ghost Felspring decided to fortify themselves at Vostok Observatory. In the Dark Age, the mountain was claimed by a Warlord known as Castor, who ruled over a village at the foot of the mountain. By the Golden Age, the observatory had been decommissioned and put under the care of the Vostok Observatory Historical Society as a public museum. During the 20th Century, Vostok Observatory was constructed atop the mountain.