So I see that people want to know how to get the secret ending. Well first things first its not so much of an ending(story) but that is all I will say about that.
In order to get this (secret sorta ending) you will have to go to each of these green boxes in order from 1 to 4 and each one within a time period of 10 seconds I think If I remember correctly. Once all of that is done you will have to make your way to the wall covered in red on this map and one of the walls should have no collision. Walk through it and you will get what you want.