Dungeon ID swapping
In vanilla ALttP, Hyrule Castle and the Sewers are considered different dungeons. When you pass through the door between the throne room and the sewers, the game changes the ID of the dungeon you're in by XORing it with 2. This is a symmetrical operation, so it creates pairs of dungeons you can swap between if your dungeon ID is not actually Hyrule Castle.
Dungeon ID swapping can allow you to collect the prize (crystal or pendant) of a dungeon without ever entering it. It's important as a way to complete Misery Mire (NL) in No Logic without having the correct medallion for it.
| Dungeon 1 | Dungeon 2 |
|---|---|
| Hyrule Castle | Sewers |
| Eastern Palace | Desert Palace |
| Tower of Hera | Thieves' Town |
| Agahnim's Tower | Swamp Palace |
| Palace of Darkness | Misery Mire |
| Skull Woods | Ice Palace |
| Turtle Rock | Ganon's Tower |
If you're in cave state, the dungeon ID becomes $FD, which is an alternate cave state in the vanilla game, and crashes in the randomizer.
Almost all setups for dungeon ID swapping (besides playing Hyrule Castle as intended) need to come from the sewers and go back and forth through the throne, so you need to do sewer door deletion first.