You can't. Well, actually there is one way, you open your map by mousing over the top right corner while on the Island, and click restart island. E)
it depends on the dungeon your talking about on poptropica. sure, there is probably one dungeon on poptropica but you still need to be specific
The dungeon on Astro-Knights Island in Poptropica is located inside the castle on the left side of the main room. You can access the dungeon by climbing down the ladder next to the statue of Mordred on the top level of the castle.
its in the dungeon.
In the dungeon
in the dungeon
go down to the last floor and click on the book that is labeled m-s
under the library in the castle
You don't or you can't
go into the dungeon
In the library, go down the stairs and go to the first library rack. there is a scroll and click on it. you will get cheese where you can feed to the rat
With the robot in the dungeon
just type in "HOW TO BEAT ASTRO KNIGHTS IN POPTROPICA" in the 'enter a Q or phrase...'!