- "That treasure chest is connected to the underground waterway... You can get out from there."
- — Jovani
The Underground Waterway is a location from The Legend of Zelda: Twilight Princess. When Link is first captured by Shadow Beasts and transformed into a wolf, he is taken to a prison in the dungeon of Hyrule Castle, which is covered in Twilight. The prison is adjacent to the Underground Waterway. It is in this prison that Link first meets Midna, when she helps him to escape. By crawling through a small tunnel, Link can leave the prison area and enter water-filled sewers, which act as a mini-dungeon, and tutorial of sorts. At the end of the sewers there is a long, spiral staircase leading to the roofs of the castle. Link can leap across the roofs and enter the tower where Princess Zelda is being held captive. Here he learns about the sad fate that has befallen Hyrule.
After completion of the Lakebed Temple, Link must return here to bring a dying Midna to Princess Zelda. The Underground Waterway can be accessed by a secret passageway in Jovani's house, which can likewise be accessed by a secret passageway in Telma's Bar. This time another area of the sewers is explored, this one requiring multiple webs to be burned with flaming sticks. This section leads back to the main sewers and subsequently, the roof and Princess Zelda's chamber. Subsequently, the Underground Waterway cannot be accessed again, as the secret passage in Telma's Bar is inaccessible, and the chest found in Jovani's house, which served as the entrance to the Waterway itself, has been filled up with treasure.