A Link to the Past
After Link defeats the Ball and Chain Trooper and rescues Princess Zelda, the two head to the Throne Room. Link and Zelda together can push the Ornamental Shelf behind the throne out of the way, revealing the entrance to the Secret Passage. The two will travel through a series of rooms that are unlit, but Link can use his Lamp to light up a series of torches.
Link will eventually reach a set of sewers where he will encounter a number of Rats, Ropes, and Keese. Once Link and Zelda reach the lit area, they will find a pair of strange walls on the west side of the screen. This secret room cannot be accessed as Link does not have any Bombs during the initial run through the Secret Passage. Link can return to the Secret Passage late in the game by falling down a secret grave within the Hyrulian Cemetery.
At the end of the Secret Passage, Link will pull a lever on the right side of the room, opening the door that leads to the Sanctuary. It is here that Link and Zelda will meet up with the Loyal Sage. Link can open the Treasure Chest found within the Sanctuary to collect a Heart Container.
A Link Between Worlds
Secret Passage from the A Link to the Past Comic