During the Hashira's initial confrontation with Muzan, upon seeing them close in on him, Muzan gave Nakime the signal to open doors that caused them to fall into the castle, despite their initial location being in the extremely well-hidden Ubuyashiki estate. You a trained demon slayer were also sent in as well

(This is where you choose where to go)

❄️ - Fight Douma 👊 - Fight Akaza ⚡️ - Fight Kaigaku 🌙 - Fight Kokushibo