Good Riddles

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?

Question: What asks but never answers?

Question: I have 6 faces and 21 eyes, but can't see a thing. What am I?

Question: What cannot be seen or felt, but can only be broken by voice?

Question: You build a house and all 4 walls are facing south. Where did you build the house?