Castle Dungeon

The Sewer Passageway is a location in A Link to the Past.

Overview
After Link frees Princess Zelda from imprisonment in the dungeon of Hyrule Castle, which has been taken over by the betraying sorcerer, Agahnim, she tells him of a way to escape safely; a secret passage in the Throne Room that leads to a Sanctuary. Upon reaching the throne room, Link and Princess Zelda combine their efforts to push aside an ornamental shelf, revealing a pitch dark tunnel that was hidden behind it. If Link doesn't possess a Lamp, the game will not allow the ornamental shelf to be pushed.

Entering the tunnel with Link's Lamp to light the way, it begins as a seemingly normal castle room, until they continue deeper, where they find themselves trudging through a sewer area full of enemies such as Rats and Keese. Navigating through this area takes Link and Zelda to a well lit room with a pair of cracked walls that Link can break down later in the game with the Pegasus Shoes or Bombs to find a considerable amount of Rupees. To get back to this room later, Link must find a secret headstone in the Cemetary east of the Sanctuary.

Climbing a staircase in the room leads to a pair of rooms with wooden floorboards, the second of which contains two switches; one is a trap, while the other opens the way to the Sanctuary. If Link pulls the wrong one, Ropes fall from the ceiling. After pulling the correct switch, Link and Princess Zelda step through to be greeted by a Loyal Sage who is waiting for them in the Sanctuary of Hyrule, and finally breathe in some fresh air.

A Link to the Past comic
The Secret Passage is also briefly featured in the A Link to the Past comic. After rescuing Princess Zelda from two Castle Soldiers that were taking her away, the young hero and the princess wind up at a dead-end, but soon afterwards one of the castle walls mysteriously opens and reveals the path to the secret passage. Using a nearby Lantern, Link and Zelda advance through the passage to eventually reach the Sanctuary.

Trivia

 * Castle Town Sewers from Twilight Princess are somewhat similar to the Secret Passage.