The stairway into the castle dungeon is opened by clicking the McM shelf on the lower aisle in the castle library.
You need the Library Slip from the Mordred Museum. Get the gold coin from the fountain outside, pay your admission, and find the Slip in a stack of books. Now the scroll in the library shelf will work, and you can enter the dungeon.
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.
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.
You have to push it open.
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.
The stairway to the dungeon is in the castle library (first floor, right side). To enter, you will need the Library Slip from the Mordred Museum. Get the gold coin, pay your admission, and find the Slip in a stack of books. In the castle library, go to the lower aisle, which is non-fiction. Click the shelf that says Mc-M and the stairway will open.
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.
it is open ing June 10 or you can buy a ticket for 500 credits
Once you have used the gold coin from the fountain to enter the Museum, and recovered the Library Slip from the stack of books there, you can open the stairway to the dungeon by clicking the lower shelf (non-fiction aisle) in the castle library. It is marked McM.
Move the Mill to open the window
you have to finish the puzzle then click on the door
"McM" is the shelf letter on the non-fiction (lower) aisle in the castle library (first floor right side). When you have the Library Slip, you can click the scroll on the "McM" shelf, and a stairway to the castle dungeon will open. (see related question)
Get the gold coin from the fountain, pay your admission to the Mordred Museum, and get the Library Slip from the stack of books. Go to the castle library (first floor right) and to the lower aisle. Press the scroll on the shelf marked Mc-M to open the hidden stairway.