Wiktionary
somewhere over the rainbow
adv. (context idiom English) at an unknown, hypothetical, or very distant place
Wikipedia
Somewhere Over the Rainbow (album)
Somewhere over the Rainbow is an album by country music singer Willie Nelson, released in 1981. It features 1940s pop standards arranged by Nelson. The album's acoustic jazz instrumentation was also meant to play tribute to one of his heroes, Belgian gypsy jazz guitar virtuoso Django Reinhardt, who influenced Nelson's playing.
Usage examples of "somewhere over the rainbow".
You're somewhere over the rainbow and the bad news is the munchkins are not fucking friendly.
Had he wished or dreamed too hard of an unattainable location somewhere over the rainbow?