In the Maid's room (castle first floor left), feed the cheese to the robot mouse.
To obtain the moldy cheese in Astro-Knights on Poptropica, you need to first find the rats in the secret dungeon. They will steal the moldy cheese from you, which you can then retrieve by using the Rat Trap item in your inventory.
you go inside, get the moldy cheese and pull the lever down.
In the undergroud part of the libary
In the Maid's room (castle first floor left) you will find a mechanical mouse.
get the moldy cheese from the basement of the castle and lay it out in the bed room
The only place is in the castle dungeon, below the library. (see related question)
you need the hovercraft,mouse,moldy cheese, owl,green glowy thing,coordinates, and find the broken paceship.
you put it in the room with the mouse in the astro knights castle and the mouse will eat it
If you mean Poptropica, you can get the rat when you go to the castle and go to the left door, give the Moldy Cheeseto the rat, and he will come to you.
There is some moldy cheese in the secret dungeon under the castle.To get the cheese:Get the gold coin from the fountain.Go in the Mordred Museum and get the library slip.Go to the castle library, the non-fiction section (lower aisle), and push on the "McM" shelf.All you can do is get the cheese and throw the switch on the wall.
There is no fish. You have to get the mouse from the madian's room and feed it to Merlin. You lure the mouse with the moldy cheese you get from the dungon.
When you get the moldy cheese from the castle dungeon, throw the wall switch that opens the rear gate to the cell. Later, you can enter through the tunnel from Mordred's lab.