Fallout 4: Vault-Tec Workshop

Vault-Tec Workshop is downloadable content (DLC) for the 2015 game Fallout 4. It mainly focuses on the workshop feature.

Vault 88 is found and under attack by Raiders and sends out a distress signal. The Sole Survivor receives the signal and frees the Ghoul Vault-Tec employee stuck in there. After doing a series of quests (or by failing them) the player eventually becomes the Vault Overseer after which the Vault becomes a settlement.

The cave can be fully explored and cleared of enemies, after which each area of the cave is fully build-able. So the player can build any underground settlement they'd like, including a complete Vault. The cave has several entrances/exits, including a Raider camp and a small pharmacy above ground.

The DLC adds a lot of new workshop items related to Vault-Tec's Vaults and the underground life.