Giallarhorn

Then spoke Gangleri: ‘Where is the chief centre or holy place of
the gods?’

High replied: ‘It is at the ash Yggdrasil. There the gods must
hold their courts each day.’

Then spoke Gangleri: ‘What is there to tell about that place?’
Then said Just-as-high: ‘The ash is of all trees the biggest and
best. Its branches spread out over all the world and extend across
the sky. Three of the tree’s roots support it and extend very, very
far. One is among the Æsir, the second among the frost-giants,
where Ginnungagap once was. The third extends over Niflheim,
and under that root is Hvergelmir, and Nidhogg gnaws the
bottom of the root. But under the root that reaches towards the
frost-giants, there is where Mimir’s well is, which has wisdom and
intelligence contained in it, and the master of the well is called
Mimir. He is full of learning because he drinks of the well from the
horn Giallarhorn. All-father went there and asked for a single
drink from the well, but he did not get one until he placed his eye
as a pledge. Thus it says in Voluspa:

I know it all, Odin, where you deposited your eye, in that
renowned well of Mimir. Mimir drinks mead every morning
from Val-father’s pledge. Know you yet, or what?

The third root of the ash extends to heaven, and beneath that root
is a well which is very holy, called Weird’s well. There the gods
have their court.


- Prose Edda, Gylfaginning