Turtle Rock (A Link to the Past)

Turtle Rock is a dungeon featured in A Link to the Past and A Link Between Worlds. It houses the final crystal containing Princess Zelda in A Link to the Past and Impa's Portrait in A Link Between Worlds. The main item obtained in A Link to the Past is the Mirror Shield, and the boss is Trinexx. In A Link Between Worlds, the Ice Rod is required to complete the dungeon, and the Bow is recommended. The final boss is Grinexx.

Entrance to the Rock in A Link to the Past
Turtle Rock is the seventh dungeon of the Dark World, and eleventh in the main game. It can only be accessed by using a warp point on the eastern peak of Death Mountain. This will warp Link to the roof of the dungeon, where he must use the Quake Medallion to open the entrance.

Entrance to the Rock in A Link Between Worlds
Turtle Rock is one of seven dungeons in Lorule, and houses a Sage's Portrait. It can only be accessed by using the Zora Flippers to speak with a large turtle in the Swamp. The Turtle will ask you to find her babies, which are located around the perimeter of the Swamp, two of which require Link's ability to become a portrait. The turtles will allow Link to access a platform with a Weather Vane. The only way for Link to access the dungeon is to use the Ice Rod on a pillar of lava, turn into a portrait and emerge on the other side.

Themes and Navigation
This dungeon is unique in that its interior looks more like an incredibly extended cavern, instead of having a man-made architecture; likewise, the Cane of Somaria (previously won in Misery Mire) shows a new function here: it creates platforms that can travel across floating rails, which help Link to fully explore this dungeon, as well as to find torches that must be lit; this also means that a lot of magic power is required (in fact, that's an advice given to Link by Sahasrahla at the start of the dungeon).

Some interesting references to the Mario series occur here as well: Chain Chomps make their debut, and warp pipes carry Link from spot to spot. Similar to the Skull Woods, there are multiple exits, one of them even leads Link to an apparently empty dead end, but guards a Piece of Heart in the Light World. But there's more: this is the only location in the game with lava, and it's harmless since Link cannot fall into it. This dungeon houses the Mirror Shield, useful to repel more powerful projectiles, and the final crystal (containing Princess Zelda) is guarded by Trinexx.

After Link clears this tough dungeon, he can access the final dungeon, which is to the west, across a bridge guarded by Lynels (where the Tower of Hera would be in the Light World).

A Link to the Past comic
Turtle Rock is also featured in the A Link to the Past comic. Like in the game, Turtle Rock is the dungeon where Princess Zelda has been imprisoned in a crystal by Agahnim.

After learning the location of Turtle Rock, Link heads there and strikes the top of it with the Master Sword to allow a lightning bolt to hit it, revealing the entrance. Inside the lava-infested dungeon, Link finds Zelda imprisoned in a crystal, but he is then attacked by a three-headed dragon. However, Roam, who had been following Link, arrives just in time to save the young hero from one of the dragon  head's attacks. Roam and Link then cut off the dragon's ice head, causing its ice and fire to mix and explode. The explosion shatters Zelda's crystal, and with the princess now rescued, the group quickly escapes Turtle Rock as it begins to collapse.

Trivia

 * In the Game Boy Advance remake of A Link to the Past, Link can warp to the Light World equivalent of the dungeon's entrance. Thanks to this, he can backtrack from Turtle Rock or even Ganon's Tower without having to traverse the body of Death Mountain again.