Bows of rain

[Aganzir]

Originally Posted by Eönwë

I'm sure there was something about that in the BoLT.

Yes, in a way - Oromë's Rainbow Bridge from Valinor to the Great Lands, but "living Men may not tread the swaying threads of Ilweran and few of the Eldar have the heart", so I don't think it can be quite compared to the Straight Road. And it was not mentioned elsewhere but in the Hiding of Valinor.