the.com/treasure trove

means A valuable find, especially a hidden or forgotten stash of something good, discovered more or less by luck.

from From Anglo-French 'tresor trové,' literally 'treasure found' — a phrase lifted straight out of medieval English law, where it named hidden gold or silver whose owner couldn't be traced. 'Trové' is the past participle of 'trover,' 'to find,' a cousin of modern French 'trouver.' The legal sense (and the crown's old right to claim such finds) came first; the cozy, metaphorical sense — a treasure trove of old letters, recipes, gossip — came later, once English speakers decided the phrase was too good to leave to lawyers.