(CNN) — In 1958, artist Yves Klein famously opened an exhibition called “The Void,” which saw him place a large cabinet in an otherwise empty room. Thousands of paying visitors turned up at a Paris ...

Art lovers were left to stare blankly after a receipt for a piece of “invisible art” sold for nearly $1.2 million at auction. The receipt, dated Dec. 7, 1959, was part of Klein’s imaginary art series ...