In 1957 a brand new Plymouth Belvedere was buried in a concrete vault outside the Tulsa County Courthouse, along with some gas, a change of oil, the contents of a lady’s purse, maps and photographs, a case of beer and various other things. Fifty years later, they dug it up—for the state of Oklahoma’s centennial celebrations.
Alas, Miss Belvedere proved to be an example of what can go wrong when you bury things. The concrete vault was built during the Cold War and was supposed to be able to withstand a nuclear attack. Alas, it wasn’t airtight or waterproof. She was found sitting in four feet of water, rusted, and with most of her upholstery rotted and the other contents of the capsule in ruins. As has been noted, there are probably better surviving examples still hanging about above-ground—a common issue with buried time capsules, particularly when the things inside can also be found preserved in libraries and museums.
Apparently the town buried another car in 1998 (again for a future centennial celebration). This time the car is all sealed up in an argon atmosphere, so perhaps his chances of surviving intact are improved.
Here is a video of Miss Belvedere when she was new. And here is an entertaining video of the unveiling of Miss Belvedere, including some short interviews with two people who were present at the burial as children.