The Secret Club's Secret is a side quest in The Legend of Zelda: Breath of the Wild. It is a quest given to Link by Greta in the Gerudo Desert. It is one of the side quests related and needed to be completed for the main quest The Thunder Helm.
The Gerudo Secret Club is only open to those who know the password. Link must find someone who knows the password to gain entry.
To get the password, Link must travel across Gerudo Town to The Noble Canteen where he will find three women chatting on the couches. If spoken to directly, they will yell at Link for eavesdropping on their conversation.
To hear their conversation, Link must go to the adjacent building to the left and stand under the vented window. After listening to their conversation, the password will be revealed as GSC◆. By returning to the Gerudo Secret Club and giving the password, Link gains entry to the club. If Link inputs the password incorrectly, however, he will have to wait at least one in-game day to try to input the password again.