Collect all of the trophies, essentially beating them game.
You get access to the Insomniac Museum. The closed door in the trophy room.
There is a teleport to Insomniac Museum. You need all trophies to open door
use gold devastator.
You have to go the opposite direction and advance until you are allowed to glide there from a very high building.
first of all you need magnet boots. then there is a wall if you keep going, if you find a ramp sort of walk up that and the gadget you get use that and go back to the door and it should be open
A portal to the insomniac museum, just like in going commando, but with info about up your arsenal instead, and I'm pretty sure it's unlocked by achieving all skill points.
the secret door is in coralines room
The duration of The Secret of the Iron Door is 1.15 hours.
there is no secret door to the snow element yet
The duration of Secret Beyond the Door is 1.65 hours.
Secret Beyond the Door was created on 1948-01-01.
Secret of the Second Door was created on 1959-12-09.