Get the gold coin from the fountain and pay your admission into the Mordred Museum. Once you have the Library Slip, go to the castle library (first floor, right) and press the shelf marked McM on the lower (non-fiction) aisle.
You click the McM place.
You will have to use the gold coin from the fountain to get the Library Slip from the Mordred Museum. Once you have it, you can click the McM shelf in the castle library and open the secret stairway to the dungeon.
In the castle library (first floor, right) there is a shelf marked McM on the lower aisle. Press it to open the secret stairway to the dungeon.
go to the secret door
There is a hidden stairway to the dungeon in the castle library, and a hidden opening under the fountain.
The secret stairway into the dungeon is on the lower (non-fiction) aisle, controlled by a scroll on the shelf marked Mc-M. You need the library slip from the Mordred museum to access the stairway. (Get the coin from the fountain, and pay your way into the museum. The slip is in a stack of books.)
You do not get or use a bucket on Astro Knights Island.
There is no treasure chest on Astro Knights Island.
Nobody know's excatly what it is except for the creators that's why its called "Secret"
No, because you need the three knights to go with you. (see related question)
Once you have the Library slip, you can press the scroll McM on the lower aisle in the castle library, which will open the dungeon stairway.
There are no bird eggs in astro knights island.