New theory by Guðrún: Bifröst laid by transcending.
Bifröst, Bilröst is the bridge we lay, layer by layer, leading to Valhöll.
We learn to “nýsa niður“, transcend the sphere of thought, by which we purify ourselves. Our purity is the very material for this bridge.
We have to understand what Valhöll is:

Valhöll is the heightened state of consciousness of a living man, an enlightened einherji, walking on earth among his fellow-men, who might not be living such an exalted state.
Val in Sanskrit means to return home, and that is what we are doing when we become enlightened. The only place where we belong.
To lay the bridge, which correlates to Sanskrit setuum stara, we transcend, við nýsum niður.

This is how we, in time, get to Valhöll.
See also Valhöll
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Listen to pronunciation: Bifröst Bilröst , Valhöll, nýsa niður, nýsta ek niður