There was one thing the gods feared and that was Ragnarok-the twilight of the gods. the gods foretold of a time when the world will sink beneath the oceans and the sun will abandon the world. Pent up magma in all the mountains of the world will erupt, spewing massive amounts of toxic plumes into the sky.
It is a series of events and disasters that bring about the destruction of the world so that a new world and a new age of gods could begin.
Ragnarök pits the gods against the forces of chaos and evil as both sides wrestle for dominance. It then ends with the loss of many lives, including the lives of many Aesir gods. This always worried Odin and he decided he was going to visit Mimir.