The Big Dig

The Big Dig is a quest in Fallout 4.

Quick walkthrough
Player character receives the quest after talking to woman named Bobbi in backstreet at Goodneighbor. She says that she's planning on breaking into Diamond City strongroom located under mayor office. At first player character needs to go down in the tunnel starting at Bobbi's house basement and help diggers fight mirelurks. After she asks player character to meet her in Diamond City and help free another member of heist team. Finally, the team go into tunnel, travelling trough metro stations and basements. After they made it underneath the strongroom and blowing the floor it reveals that it's not Diamond City's strongroom but the storage room owned by John Hancock, the Goodneighbor's mayor. Player character has a choice of persuading Bobbi to leave, kill the guards or betray Bobbi and kill her instead.