What to know

  • The Exhaust Organ is a unique area in the Bilewater region in Hollow Knight: Silksong.
  • There is a bench and a lost flea hidden in the northwest corner of the Exhaust Organ room.
  • Accessing the area usually requires double jump, wall jump, and glide abilities.
  • Defeating the local Phantom boss unlocks useful upgrades and new traversal paths.

After a challenging trek through the poisonous Bilewater section of Hollow Knight: Silksong, you’ll come across the Exhaust Organ—a large, imposing room filled with platforming puzzles and secrets. This spot marks a crucial checkpoint in your journey through Bilewater and hosts several collectibles and unlocks that can make future progress much smoother.

Exhaust Organ Flea: Navigating to the Exhaust Organ

To reach the Exhaust Organ, start from the Whispering Vaults and head left. Make your way through several hazardous chambers until you find a large room featuring the Exhaust Organ centerpiece. This area is best tackled after acquiring the double jump, wall jump, and glide abilities—these unlock new vertical and lateral paths otherwise inaccessible in Bilewater.

Once inside, you’ll notice a bench, which acts as a welcome respite and a map update station. Navigating the northwest section of the room, use your new movement skills to reach elevated platforms and breakable walls. The lost flea is tucked away on a ledge above brambles and poison pools, requiring careful platforming and perhaps creative use of environmental objects.

Exhaust Organ Flea: Map & location

Exhaust Organ Flea: Finding and rescuing the lost flea

Fleas in Silksong are scattered throughout Pharloom, much like grubs in the first game, with a handful located in the lower regions of each main area. The lost flea near the Exhaust Organ marks one of the trickier ones to reach early in your Bilewater exploration. When you get close, you’ll hear a faint whining sound—a clue to its presence.

To rescue the flea:

  • Use double jump to ascend to the upper left.
  • Break brambles that hold the flea captive.
  • After freeing it, this counts toward progress in the Lost Fleas Wish quest.
  • Report back to Fleamaster Mooshka’s caravan for a reward. For every five fleas rescued, you'll receive Flea Brew charges, improving movement and attack capabilities.

Exhaust Organ Flea: Reward and implications

Defeating the Phantom boss in the Exhaust Organ area nets you the Cross Stitch parry ability and opens a shortcut elevator to The Cauldron—streamlining future travel in Bilewater. This room also hides other collectibles, like the Quick Sling tool on a nearby route, and several lore tablets.

The strategic placement of the bench here is helpful for adventurers seeking to plan ahead before tackling deeper Bilewater challenges or returning to earlier sections to search for more fleas.