Bifrost

Then spoke Gangleri: ‘What way is there to heaven from earth?’

Then High replied, laughing: ‘That is not an intelligent question.
Has no one ever told you that the gods built a bridge to
heaven from earth called Bifrost? You must have seen it, maybe it
is what you call the rainbow. It has three colours and great
strength and is built with art and skill to a greater extent than
other constructions. And strong as it is, yet it will break when
Muspell’s lads go and ride it, and their horses will have to swim
over great rivers. That is how they will advance.’

Then spoke Gangleri: ‘It does not seem to me that the gods built
the bridge in good faith if it is liable to break, considering that they
can do as they please.’

Then spoke High: ‘The gods are not deserving of blame for this
work. Bifrost is a good bridge, but there is nothing in this world
that will be secure when Muspell’s sons attack.’

Then spoke Gangleri: ‘What did All-father do then, when
Asgard was built?’

[...]

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. Every day the Æsir ride there up over Bifrost. It is
also called As-bridge. The names of the Æsir’s horses are as
follows: best is Sleipnir, he is Odin’s, he has eight legs. Second is
Glad, third Gyllir, fourth Glær, fifth Skeidbrimir, sixth Silfrtopp,
seventh Sinir, eighth Gils, ninth Falhofnir, tenth Gulltopp, Lettifeti
eleventh. Baldr’s horse was burned with him. And Thor walks to
the court and wades rivers whose names are:

Kormt and Ormt and two Kerlaugs, these shall Thor wade
every day when he is to judge at the ash Yggdrasil, for
As-bridge burns all with flame, the holy waters boil.’

Then spoke Gangleri: ‘Does fire burn over Bifrost?’

High said: ‘The red you see in the rainbow is burning fire. The
frost-giants and mountain-giants would go up into heaven if
Bifrost was crossable by everyone that wanted to go. There are
many beautiful places in heaven and everywhere there has divine
protection round it. There stands there one beautiful hall under
the ash by the well, and out of this hall come three maidens whose
names are Weird, Verdandi, Skuld. These maidens shape men’s
lives. We call them norns.


- Prologue, Gylfaginning