To reach the Putrified Ducts in Hollow Knight: Silksong, players must follow a specific and somewhat hidden route originating from the Memorium area. The lower section of the Putrified Ducts can be entered from Bilewater, but the majority of the zone requires a separate path. Within the accessible lower part, you’ll encounter the Broodfeast quest and locate the Key of Apostate.
Begin by traveling north from the Grand Bellway until you reach the top, where you can enter Memorium. A double jump is essential to ascend the platforms and gain entry. Once inside Memorium, jump to the platform with the lore board, then leap to the next platform above. This brings Hornet to the second tier, where the path divides.
Head right to a zone teeming with various enemies, including small and large spiders. After fighting through, you’ll face a mini-boss near the end of the corridor. You can choose to battle or bypass it to quickly pass through the door. Descend carefully, avoiding rolling foes as you drop down the platforms.
Proceed through the door marked by a hanging sign to enter an apparently empty room. Move further inside and look upward to spot a narrow tunnel. Use double jump and Clawline to climb higher and advance onto a bridge.
At the bridge’s end, you’ll find a tall wall that can be scaled with a combination of cling grip and double jump. Between the walls lies a destructible barrier—attach Hornet to the wall and break the rocks to reveal the passage.
Continue right into a dim tunnel, steering clear of spikes, and you’ll eventually arrive at the Putrified Ducts. This area closely resembles Bilewater, featuring maggot-filled swamps that deplete Hornet’s silk. Fortunately, there’s an item nearby that temporarily shields you from the swamp’s effects. Additionally, an NPC can assist in revealing the locations of missed fleas throughout Pharloom.