The Ancient Vault is located in the center of the Northern Territory where Percival searches with Perkins.
Percival and Perkins journey here at the request of Percival. They ask Zoey to make a bomb to destroy the lock, which blows off the whole door. When they look inside, they are disappointed that it only holds a couple of trinkets (marbles, spinning jacks, etc.).
The description is likely a reference to Fallout, a series of post-apocalyptic role-playing video games. Enormous fallout shelters known as Vaults are present in every game and the inhabitants of these vaults are collectively referred to as Vault Dwellers.