Church bells...
In 2013, a man from Czech Republic was digging up his backyard to install some pipes when he stumbled across unusual metal objects. After excavation, he found out it was 2 large church bells about 400 years old. Later, it turned out that the bells were stolen 11 years earlier from a nearby church. The thief who buried them might have attempted to hide them but for some reason, didn't get to retrieve them.