Croatia

In Istria, the Mirna River, which flows near Buzet, is the axis of land called "the kingdom of truffles."

An excerpt from the article 51 facts about Croatia
Truffles are hard to find as they grow underground. Therefore, they are sought out with the help of dogs (in France and Italy - trained pigs). The largest truffle in the world so far, registered in the Guinness Book of Records, weighed 1.31 kg and was found in November 1999 near Buzet by Giancarlo Zigante and his dog Diana.