The City Vault holds the Mayor's prized GIANT DIAMOND. Other than that, it's just another useless location. Then Jane stole it, and blew the building apart, so it's uselessly crappy now anyways.
Underneath it, is a secret basement which Ginger hid her vessel in whilst she engaged in 12th dimensional activities.
FAR underneath the dirt of the basement, there was a secret, dimly lit room, containing 10 opposouls.