Boss Lock

Boss Locks are special locks to the bosses in The Legend of Zelda series that requires Link to find a Boss Key, also known as a Big Key. Once Link is in the boss room, he can't exit, most of the time. Most of locks within each game all share a similar appearance,

A Link to the Past
The Big Key was first introduced in A Link to the Past. However, these keys could be used multiple times. They unlocked large chests and special doors. One of the locked doors was always at least a few rooms away from the Dungeon Boss.

Link's Awakening
Link's Awakening marks first appearance of true Boss Locks. The locks are opened with a Nightmare Key. Every level has a Nightmare Key and a Boss Lock right before the Boss Room.

Ocarina of Time
In Ocarina of Time, the Boss Locks are slightly different. In the first three levels, there are no Boss Keys in the dungeons. There are only puzzles in the room prior to the boss. A fair portion of each level is dedicated just to solving the puzzle in these rooms, and they typically require items or information from another part of the dungeon. In the last six levels, the five temples and Ganon's Tower, there are Boss Locks and Boss Keys. They function similarly to the keys and locks in Link's Awakening.

Majora's Mask
In Majora's Mask, the four temples all have Boss Locks. They function in the same manner as the ones in Ocarina of Time. The final level has no Boss Locks in the traditional sense. But there are five children running around. Link can either choose to talk and "play" with all of them to gain a useful tool, or he can talk to the child wearing Majora's Mask to proceed directly to the final battle.

The Wind Waker
In The Wind Waker, every single level has a Boss Lock. They function in the traditional manner.

Twilight Princess
The locks are all very similar except for the bedroom lock found in Snowpeak Ruins in Twilight Princess. Every level has a Boss Lock. They function like those in previous games.

See also:
 * Bar Lock
 * Locked Door