Probably old question, but...(secret endings help)

In ASD, there is a tower close to your house. Jump from there, but don't go up, go under.
In UwA, check the walls in the hallway before the bomb.

I'm assuming you mean the tower to the left of the house in ASD, where you can jump to the cloud area. I don't see anything to go under.
What part of the hallway are we talking about in UwA? I've gone over every inch of it after the last set of traps (when the tunnel goes out of the water, then several screens right, then drops back down to the bomb area).

When you fall down and go right to get into the bomb area, you have to set the bomb once or twice and then go back into the hallway. There'll be a secret passage then.

Set the bomb as in make it go off? Or press the first couple of correct buttons? Because when I do the latter there's a laser beam in the way.