This is the Octobasse, it was invented in 1850 by French violin maker Jean-Baptiste Vuillaume. It has three strings and stands roughly 3.48 meters tall (11.4 ft). Because of the extreme fingerboard length and string thickness, the musician plays it using a system of hand and foot-activated levers and pedals.

In this video we get an up close and personal with the octobasse that is on display at the Musical Instrument Museum in Phoenix, Arizona.