There are several doors on several islands.
A few are :
(see related questions)
TO get into the asteroid castle you have to complete the puzzle on the door.
if you go past the cat person on the right there is a door you play the color combo on the door on your pipe (get it in the museum) and then talk to the guy and go in the door
on spy island you put the chameleon suit on and go to the docks and get past the B.A.D guys and get to the door
Simply type OPEN. at the top of the entrance, there is a translation key. press the word in hieroglyphics.
you can not get the cat away from the door on poptropica you have to jump over it
how do you get past hte heiroglyphics in shark tooth island on poptropica
you have to jump
you can find it in early poptropica
you open the door of the ship in poptrpoica
there is a mummy but you dont get past it
scream at it!
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