A day came where Odin "sacrificed himself to himself" by hanging on the world tree Yggdrasil for 9 days and nights. He hanged there without food or nourishment. From this he gained the secrets to existence.
It is time for me to hang here for 9 days and 9 nights and only then will I acheieve the secrets of existence.
After Odin had learned the secrets of existence he decided to go and have a challenge with one of the wisest giants. Whoever was the victor, took the others head. Odin won by asking the Giant a secret about existence that only Odin himself would know.
How can this be? I'm one of the wisest Giants around and I did not know the answer! You may now take my head.
You did not know the answer to my question. This makes me the victor and I will now take your head.
Odin had heard news that his son had got in to some trouble with a dead seeress. He traveled to the underworld to confront and consult this dead seeress on behalf of his son.
Oh Seeress! What has my son done that concerns you? Please tell me the problem .
Oh Odin! Your son has involved himself with me and now you must consult me on what he has done on his behalf.