If you didn't know already (and you probably didn't), it's the 500th anniversary of a very large, piano-like musical instrument played with fists and feet called the carillon. And the University of Denver has one that you've probably heard, chiming like church bells. The woman behind the ringing is Carol Jickling Lens, who has spent her career traveling around the world to play the instrument, including during a recital in England where Princess Margaret dedicated a plaque to her. A cross North America, there are 170 carillons, including the one at DU's Ritchie Center tower, which houses 65 bells, the largest weighing six tons. "A lot of people have no idea; they think it's all automatic," Jickling Lens, who usually plays the bells on DU's campus around noon every day, tells 9News. There's generally no discernible audience, but on Sunday she played an hour-long recital for about 20 people. She'll play another concert August 8 and then again in December for the holidays.