Answer:
I go through a door but never go in, and never come out. What am I?
I am a path between high natural masses; remove the first letter to get a path between man-made masses.
I am like thunder in your cranium
I am a rock group with four members. All dead one was assassinated.
I can be simple or I can be complex. I can be found in this riddle or in everyday life. I can be shapes or even colors.
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.