Hyrule Castle Tower/No Logic

Getting there

You will usually enter the tower through its front door, which requires the master sword or the cape.

You can also reach the top floor of the tower by carefully performing a west subtile YBA from the hourglass-shaped room in Misery Mire ^(NL). Perform the YBA (toward the room with the wizzrobes and the big key door), back out exactly 2 or 3 pixels, then transition west through the door.

Getting around

You don't need any keys to open the two chests. A north subtile YBA in the first door will bring you to the 2F dark room, skipping the first key door.

With this, you can also reach the Agahnim fight with only one key.

Where you can go

You can clip out of the Agahnim fight with a bomb to reach Hyrule Castle Escape ^(NL). This is useful for dungeon ID swapping.

Illustration of the clip

Getting a dungeon prize from Agahnim

If you are in another dungeon's state when you defeat Agahnim, you can receive that dungeon's prize. It is reported that you then have to walk inside a building before you save and quit, or else SRAM will be corrupted in a way that deletes your save file.