First of all, the staircase is in the Castle's library, which is the door on the right. Below the platform where the librarian guy is walking, there's a lower level with a whole bunch of signs with letters on them. Find the sign that is labeled NON-FICTION. Just to the right of that, there's a shelf. If you look closely on the shelf, you'll notice above the McM sign, there is a green brick. Click it, and a staircase will be revealed. Good luck!
There's a lock under the hay in Astro Knights
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 fountain. you have to find the password first.
go to the secret door
The secret room between the hay bales!
There is a secret society inside the fountain in the Town Square. You get the code from the creepy girl in the Mill.
The small key in Astro Knights Island is for Mordred's secret hideout. When you come to that wind mill area, move the hay bales apart and use the key on that.
Go to the library and click on Mc. It will reveal a secret passageway.
No, because you need the three knights to go with you. (see related question)
Go inside the castle and go to your left.The secret message is by the mirrow
Nobody know's excatly what it is except for the creators that's why its called "Secret"
When you have all three of the Knights together, you will travel to the secret hideout of the Binary Bard in the Asteroid Belt. (Secret location : X-11 Y-82)