The hidden stairway to the castle dungeon is under the library (first floor, right). Get the gold coin from the fountain and pay your admission to the Mordred Museum. In the stack of books is a Library Slip. Once you have it, you can press the Mc-M shelf in the lower aisle of the library, to access the hidden dungeon entrance.
There is a hidden stairway to the dungeon in the castle library, and a hidden opening under the fountain.
You do not get or use a bucket on Astro Knights Island.
There is no treasure chest on Astro Knights Island.
The hidden stairway to the castle dungeon is in the library (first floor right). You will need the Library Slip from the Mordred Museum. (Get the gold coin from the fountain to pay your admission.) Once you have the library slip, press the scroll on the shelf marked Mc-M on the lower aisle, and the stairway will open.
There are no bird eggs in astro knights island.
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.
its on the island
There is no well at the mill. There is, however, a rope, and a secret society member, and a hidden hovercraft.
Which one of many?
How do you talk to the girl in the hay loft at astro knights island?
The manure is used to power the hovercraft hidden in the attic of the mill. (see related question)
You click the McM place.