When you enter the dungeon from the library, and get the cheese, you should throw the switch on the wall. It opens the small back gate to the dungeon, from which a passage extends to Mordred's underground laboratory. Although you cannot return to the dungeon through the library anymore (its guarded), you can come in the "back way".
(see related question)
Actually, Merlin has little to do on Astro Knights Island. He recovers the fuel rod from the dungeon when the robot self-destructs. And he battles Mordred at the very end of the island.
In Mordred's underground lair, there is a way blocking the tunnel to the back of the dungeon. But it isn't rock, only dirt, and can be pushed through will a little effort.
go back up the stairs or back through the little hole
Leave the dungeon with the cheese and go to the Maid's room (castle first floor left) to get the mechanical mouse and the Secret Message. The message goes to the girl in the second floor loft of the Mill. With the Cosmic Symbols card, you can enter the hidden room under the fountain and get the key to the underground door between the hay bales. (see related question)
First you go to modreds library and get the slip ( you get the gold coin by going to the fountan ) then you go to the castles library and go down the little stairs. there will be a sign that says m-s. a little to the left there will be a smaller sign that says mcm. click that. hope that helped a lot
It's just a cool little event location, it really has no use.
really all you have to do is read them they should help a little bit the island
The wall in Mordred's underground lab is made of DIRT not rock, and with a little effort you can push right through it. The tunnel leads to the back entrance to the castle dungeon. (You should have already opened the gate when you threw the switch and got the cheese.) (see related question)
first go to thelibrary in the castle. then go down the 3 or 4 steps. there will be a shelf click on the left side of it and a stair case will appear
You have to go back into the dungeon by way of Mordred's underground lab. Once you have fed the mouse to the robot owl, push down the dirt wall and go left. In the jail cell, the alien robot will self-destruct. Click the owl and then click the little green fuel rod. The owl will bring it to you.
im not sure but i think there is a little bit more than blizzard island
The switch in the dungeon (the library entrance) opens the little gate in back of the cell. That's how you get into the cell. The tunnel leads to Mordred's secret underground laboratory, and you'll need a key to get in there.