From Longman Dictionary of Contemporary Englishcrown jewelˌcrown ˈjewel noun [countable] 1 → the crown jewels2 the best or most valuable thing that a person or place has Innsbruck’s crown jewel is the old town centre.
Examples from the Corpus
crown jewel• Innsbruck's crown jewel is the old town center.• The petrochemical division of Pemex was seen as the crown jewel of the privatization frenzy.• But the crown jewel of the disk is the 25-minute Clarinet Concerto, by Richard Faith. 