Marcel Duchamp's "Readymades" were a group of his artwork that were created with mass-produced objects, taken from their original purpose and created into art. One example of this is his "Bicycle Wheel" piece, where he combined a wheel and a stool to create a piece of art that has been analysed by the public to this day.
Another common piece that has been raved about over time is his "Fountain". For this artwork, Duchamp used a common urinal signed with the fictitious name of "R.Mutt", turned it upside down placed it as a showcase piece. Nothing major was altered about the object, however automatically, the urinal increased in value as it was deemed as a piece of art.