The Great Door West

* The Great Door West is the door that links Ruins to the Mt. Ebott pit bottom. It also opens to the outside world and was the first door to be open. But for some reasons, monsters never tried to climb the pit up. 

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* This is the door that humans cross after they fell down the pit to enter in the Underground. Asriel met Chara at this place where later Firsk met Flowey and Toriel. 

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* The Great Door West works in harmony with the Great Door East, that remains at the cavern end, in the King's castle and opens on the outside world. 

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* The magic of the Doors is a "one way door": it only allows people to cross only from one side but not the other. There is a few other small doors working the same way in the Underground, such as the Forest Door.