Sub-Level 13 is a location in Borderlands: The Pre-Sequel. It can only be accessed after accepting the Sub-Level 13 mission from Pickle. There are rumours that it is haunted.
Borderlands Pre Sequel - Cult of the Vault (Sub-Level 13)
Vault Symbols-Sub-Level 13 (borderlands TPS)
Sub-Level 13 Chests Guide