Head over there and meet with Shaw and listen to what he has to say. Speak with Preston after completing a few Recruitment quests and he mentions someone named Ronnie Shaw who is at the Castle. You can find ammo in the Castle’s interior corridors.

You can pick up a magazine near the central radio mast. How you take the Castle is up to you but focus on clearing the courtyard first. You can do the following to retake the Castle: Meet with members of the Minutemen who want to know your plan of attack. Go to the remains of Ivan’s snack shop outside the Castle, South Boston.

Once the Minutemen are set up at the Sanctuary and you completed a few Radiant quests ( Ownership, Recruitment), Preston Garvey wants to retake the Castle. You can keep giving her the chems to hear her visions or use Charisma (Medium) to convince her to go clean. The next time you meet her, she asks you to build her a wooden chair. If you have some, offer her but if you don’t, find her the chems she needs. When you speak with her, she asks for some Jet.

However, to keep them flowing you need to get her some chems and she needs 8 hours of sleep between each intake. Mama Murphy claims she sees visions of the future. Also, build a water purifier, and feed them. Access your workshop and make new beds, furniture inside new or pre-built structures. When Preston Garvey comes to the Sanctuary, they want you to build the Sanctuary. Also, agree to join the Minutemen at the Sanctuary. If there are remaining Raiders, clear them out and meet with Preston for a reward. You will need Fusion Cores to run it but if you don’t have any, detach its Minigun. On the roof of the museum, you will find an empty T-45 Power Armor. Loot everything in sight, you can pick up Fusion Cores, Vault-Tec Bobblehead, and a classic issue of RobCo FUN! inside the museum. Use the bobby pin or hack the terminal to open the security gate. Once you are done, drop to the ground floor and reach the basement.

Where is the castle in fallout 4