Koenig's main work and most famous work is "The Sphere". The world's largest bronze sculpture of modern times once stood on the plaza beneath the two World Trade Center towers in Lower Manhattan until the terrorist attacks on September 11, 2001. The artifact, weighing more than 20 tons, was the only remaining work of art to be recovered largely intact from the ruins of the collapsed twin towers after the attacks. With its damage deliberately left unrepaired, the sculpture now stands in Manhattan's Liberty Park as a memorial to the victims of the September 11 attacks.