Wiktionary
holy grails
n. (plural of holy grail English)
Usage examples of "holy grails".
When she reappeared, she was holding out in front of her, as if they were twin holy grails, a pair of pumps that seemed to have been fashioned from passion fruit and monkey entrails knotted together in posh bows.
To Keff and Carialle, the designation meant that most elusive of holy grails, an alien race culturally and technologically advanced enough to meet humanity on its own terms, having independently achieved computer science and space travel.
So I kind of tried to make sure that the folks working on the condemnation proceedings in the District Court wouldn't climb up onto any white horses and go after any holy grails.