Where abouts is the door that you need to use the encoder from the 'secret stash'?

Also, I have completed the game by going to the Monolith and making a 'secret wish' and the guy wishes for money (dunno why, I have over 100K), and he imagines it all and dies, which was rubbish, such a terrible end to the game. Without giving away too much, is there another ending associated with the Monolith, or do it need to go somewhere else, e.g. the secret door for another ending?