Cappy in a Haystack

Cappy in a Haystack is a quest in the Fallout 4 add-on Nuka-World.

Detailed walkthrough
Between the Parlor Dinner Theater and Fizztop Grille, Sierra Petrovita is encountered talking to a raider. Intercepting the conversation reveals that she has come to find the reward for finding hidden Cappys throughout the park. Given that the reward was meeting the creator of Nuka-Cola, she figures that in his office might be the original recipe for the drink. She gives her sunglasses to you before leaving. Once you get close enough to a marker, it disappears, encouraging the thorough search of an area.

Fizztop Grille
One is west of the Fizztop Grille, on the large wall beside the restrooms building.

Safari Adventure
The first Cappy in Safari Adventure is through the hedge maze beneath the treehouse, against a wall on the eastern edge. From the entrance, the order of turns is: right, right, left, left, and right. Watch out for the gatorclaws. The second is just outside the Primate house, on the back of the gorilla statue to the right of the door.

Dry Rock Gulch
The Dry Rock Gulch section has two; The first is located on the back of a gravestone next to the Giddyup Kid protectron. Another is located within the Mad Mulligan's Minecart Coaster, on the wall of a little shack beside the waterfall.

Galactic Zone
In Galactic Zone, there are two. The first is at the entrance to the dead traders' camp around the back of Star Control entrance. The sign should be on the left side entrance. The second is up the ramp right next to the exit door of the RobCo Battlezone. Turn right immediately at the top of the ramp, and the Cappy is on the wall near the trash bins.

Kiddie Kingdom
There are two in the Kiddie Kingdom. One is in the Fun House in the turntable room, second door on the left when entering from the topsyturvy room. The second one is located right next to the moat to King Cola's Castle, up a stone staircase and into a destroyed wooden clocktower.

World of Refreshment
In the World of Refreshment, One is on the two story building across from the Nuka Wild sign in the wild west setting.

Return to Sierra Petrovita and use the keypad. In the office, there is a button behind the Nuka-Cola machine. This unlocks a vault to the head of the inventor. If one chooses to shut off the power and open the door, the head dies. Behind the door is a Nuka-nuke launcher as well as pre-War money, various Nuka-Colas, and some other loot.

If you pick the Nuka-World jumpsuit, you can still shut off power to Bradberton's head, and the door will open, though this causes Sierra to become hostile.

Bugs

 * Once after taking the elevator to the vault and following Sierra up the stairs Sierra will become stuck in the corner of the the stairwell. To fix this go completely out of the office and into Nuka-Town then re-enter building and return to the vault. Sierra will be talking to the founders head and you can continue the quest. PC players can also use the "moveto player" console command to teleport her out of the corner and she will continue her path towards the door.