Curie is one of the seven romantic friends you can find in Fallout 4. She is erudite, gentle, and sassy, named after the physicist who discovered radioactivity.

Unlike other romance candidates like Piper or Cait, Curie is a bit tricky to find. She’s locked away behind the Vault 81 quest, Hole in the Wall. You’ll need to find the optional vault and successfully complete the quest chain to recruit her into your party of companions. So, here’s how to get started.

Vault 81 is unique in that it is the only Vault in Fallout 4 that is not overrun with enemies. Instead, it functions as a small NPC settlement in its own right. It can be found east of Diamond City by following a path uphill from Chestnut Hillock Reservoir to a fenced-off scrapyard. The cave beneath the scaffolding serves as the main entrance to the vault.

Entering the cave and inserting your Pip-boy into the interface will draw you into a somewhat hostile conversation with the chief security officer. After some back and forth, you’ll be asked for three Fusion Cores in exchange for access to the vault. You can bypass this with a fairly difficult Charisma check, but you won’t get the 100 caps reward for retrieving the Fusion Cores.