Anri Sala built an outdoor sculpture - a distorted clock - in beautiful Karlsaue for dOCUMENTA (13). There are actually two ways to see Sala's clock: at Karlsaue and through a telescope in the Orangerie. Like many other visitors, I missed the view through the telescope. I remember seeing at the Orangerie, some 2 km away from Sala's work, an old landscape painting with a real clock embedded in it. While the landscape was painted in perspective, the embedded clock looked awkward and clearly didn't fit. On reading some information afterwards, I realized that Sala's clock, built distorted to appear like one in perspective, was supposed to correct the perspective of the clock in the painting - a subtle but clever idea. It's distorted but actually tells the correct time!
Sala at Karlsaue, Kassel 2012: