You are looking for a cowbell alongside Highway 28 in Belle, MO. 
This particular cowbell is 15 feet tall, 12 feet wide, and 8 feet deep, and weighs 6,300 pounds! The clapper of the bell is a 350-pound wrecking ball, and I'm told the bell does ring, although I didn't crawl inside to try it. It is believed to be the world's largest cowbell, and has been submitted to the Guinness Book of World Records for verification.
The cowbell was created by a local business owner to bring attention to Belle, a community of 1600 people. The new Rock Island Trail State Park (under development) is just north of the site. Passersby on Highway 28 are welcome to pull into the business’s parking lot to take photos and admire the bell. The cache is not ON the bell, but it is nearby, and the business owner has approved the location.