Mimer watched over the so-called Mimer's well, the fountain of wisdom. which lies at one of the three roots of Yggdrasil. At the root that leads to Jotunheim - the realm of the giants. He not only guarded the spring, but cleaned and picked fallen leaves from it. The source is magical, whoever drinks from it gains the ability to see and hear everything that has happened and everything that will happen in the world. Mimer drank every day and is therefore very wise