This page is a room-by-room breakdown of Forbidden Underground Waterway. All "recurring features" of a given room — namely, enemies that respawn whenever the room is reentered and blue chests that self-refill whenever the zone is exited and reentered — are listed in bold above one-time collectibles and events. All chest icons shown in the map screen below are the zone's blue chests.
- Screen 1:
- ×3 Bat, ×2 Buer
- ×∞ Dullahammer Head (Hard)
- Exit to Garden of Silence
- Breakable wall containing MP Max Up
- Bookcase about Crimson Storm technique
- Screen 2:
- ×3 Bat, ×3 Buer
- Green chest containing Elemental Ammunition/R (requires Double Jump)
- Screen 3:
- Screen 4:
- ×2 Decarabia, ×1 Bat, ×1 Shovel Armor
- ×1 Bat, ×1 Demon (Hard)
- Screen 5:
- ×1 Chair Mimic
- Blue chest containing Ruby, Sapphire, Emerald, and/or Rennet
- Capacity upgrade
- MP Max Up
- Breakable wall leading to Screen 7 (May require Double Jump)
- Breakable wall containing Capacity upgrade
- Green chest containing Curry Powder (mostly requires Double Jump, though you can also ride the Chair Mimic)
- Exit into Screen 6 (requires Double Jump or riding Chair Mimic)
- Breakable wall leading to Screen 8
- Screen 6:
- Green chest containing Curry Dish/R
- Screen 7:
- Benjamin Judd's second appearance (give Waystone for 5,000G)
- Screen 8:
- Green chest containing Critical Ring
- Screen 9:
- Screen 10:
- ×4 Forneus, ×3 Bat, ×1 Shovel Armor
- 2 blue chests containing Ruby, Sapphire, Emerald, and/or Rennet (requires Deep Sinker)
- Screen 11:
- ×3 Bat, ×2 Toad, ×1 Buer, ×1 Shovel Armor
- ×∞ Dullahammer Head (Hard)
- Bookcase about Sansetsuzan technique
- Breakable wall containing MP Max Up
- Screen 12:
- Screen 13:
- ×3 Toad, ×2 Shovel Armor, x 1 Demon
- ×3 Bat, ×1 Buer (Hard)
- Screen 14:
- ×4 Buer, ×4 Toad, ×2 Bat, ×1 Shovel Armor
- ×6 Bat, ×2 Demon (Hard)
- 2 blue chests containing Ruby, Sapphire, Emerald, and/or Rennet
- Red chest containing 500G
- Green chest containing Fish Dish/R (Requires Double Jump-kicking off lanterns)
- Screen 15:
- Locked door that can only be opened by a lever from the side of Screen 32
- Screen 16:
- ×1 Demon
- Green chest containing Traverser's Ring
- Screen 17:
- ×2 Shovel Armor, ×2 Bat, ×1 Buer
- ×2 Bat (Hard)
- HP Max Up
- Screen 18:
- ×1 Shovel Armor, ×1 Demon, ×1 Decarabia, ×1 Buer Armor
- ×2 Bat (Hard)
- Breakable wall containing Voice Changer
- Screen 19:
- ×7 Buer, ×3 Buer, ×∞ Dullahammer Head
- ×∞ Malediction (Replaces Dullahammer Head on Hard)
- Screen 20:
- Exit to Entrance
- Screen 21:
- ×5 Bat, ×2 Axe Outsider
- ×12 Water Leaper (Hard)
- Exit to Entrance
- Screen 22:
- ×3 Bat, ×2 Water Leaper, ×1 Archdemon
- Bookcase about Penetrate technique
- Screen 23:
- Screen 24:
- ×2 Bat, ×1 Buer
- ×4 Water Leaper (Hard)
- Screen 25:
- ×3 Bat, ×3 Forneus
- 2 blue chests containing Crystal, Fried Fish, Mahogany, and/or Platinum (one chest requires Deep Sinker)
- Exit to Arvantville
- Screen 26:
- ×4 Buer, ×∞ Malediction
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum
- Green chest containing Rose Ring
- Breakable wall containing Critical Ring
- Screen 27:
- ×4 Bat, ×3 Water Leaper, ×1 Archdemon, ×1 Shovel Armor
- Screen 28:
- ×1 Shovel Armor
- ×10 Bat (Hard)
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum
- Screen 29:
- Screen 30:
- ×3 Water Leaper, ×3 Bat, ×1 Poison Toad, ×1 Archdemon
- ×1 Archdemon (Hard)
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum
- Screen 31:
- ×7 Bat, ×1 Water Leaper, ×1 Archdemon
- Breakable wall containing Capacity upgrade
- Screen 32:
- Narrow path requiring Reflector Ray to pass
- Screen 33:
- ×2 Bat, ×4 Deeseama, ×1 Glashtyn (Aqua Stream shard drop from Deeseama is mandatory)
- ×2 Bat (Hard)
- Screen 34:
- ×3 Bat, ×1 Water Leaper
- ×1 Archdemon (Hard)
- Screen 35:
- Screen 36:
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum (requires Deep Sinker)
- Screen 37:
- Screen 38:
- Screen 39:
- ×2 Scylla
- ×2 Scylla, ×1 Forneus (Hard)
- 2 blue chests containing Crystal, Fried Fish, Mahogany, and/or Platinum (requires Deep Sinker)
- MP Max Up
- Screen 40:
- ×1 Glashtyn, ×1 Forneus
- ×1 Scylla (Hard)
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum (requires Deep Sinker)
- Green chest containing Strider Belt (requires Deep Sinker)
- Red chest containing 500G (requires Deep Sinker)
- Screen 41:
- Exit to Hidden Desert
- Screen 42:
- Exit to Hidden Desert
- Screen 43:
- ×1 Water Leaper, ×1 Archdemon
- ×1 Archdemon (Hard)
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum
- Screen 44:
- ×1 Macaron
- Green chest containing Ultimate Dish/R
- Screen 45:
- Green chest containing Faerie Scarf
- Roadblock requiring Invert
- Breakable wall containing Supreme Dish/R
- Screen 46:
- ×1 Seeker, ×1 Archdemon
- ×2 Water Leaper (Hard)
- 2 blue chests containing Crystal, Fried Fish, Mahogany, and/or Platinum
- Screen 47:
- Green chest containing Steel Lightning
- Screen 48:
- ×2 Water Leaper, ×2 Bat, ×2 Seeker, ×1 Archdemon
- ×1 Archdemon, ×∞ Malediction (Hard)
- Breakable wall containing MP Max Up
- Screen 49:
- ×3 Bat, ×3 Water Leaper, ×1 Seeker
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum
- Screen 50:
- ×1 Archdemon, ×1 Axe Outsider, ×1 Seeker
- Screen 51:
- ×2 Bat, ×1 Forneus
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum (requires Deep Sinker)
- Screen 52:
- ×1 Seeker
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum
- Screen 53:
- ×2 Deeseama, ×1 Glashtyn (Aqua Stream shard drop from Deeseama is mandatory)
- ×5 Deeseama (Hard)
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum (requires Deep Sinker)
- Breakable wall leading to Screen 55
- Screen 54:
- Screen 55:
- Screen 56:
- ×2 Glashtyn
- Roadblock requiring Deep Sinker and Reflector Ray shards to pass
- Screen 57:
- ×3 Scylla, ×1 Seeker
- Blue chest containing Crystal, Fried Fish, Mahogany, and/or Platinum (requires Deep Sinker)
- Exit to Secret Sorcery Lab
- Green chest containing Swordfish
- Breakable wall containing Plunderer's Ring
- Screen 58:
- Exit to Inferno Cave