South Vegas ruins is a location in the Mojave Wasteland.
Quite a few members of the Fiends gang dwell here, and Vault 3, their "home" is also located here. Zapp's Neon Signs is a building to the north, housing Fiend leader Duke. Entrance to the ruins can be gained near the Poseidon gas station and it has an exit to Fiend territory.
The South Vegas ruins appear only in Fallout: New Vegas.