The Dutch city of Rotterdam was nearly totally destroyed during World War II and left as rubble,after which it was quickly rebuilt by erecting many concrete shoebox-style buildings. To counter this impersonal and monotonous architecture, a group of artists decided to create a bunch of interesting and offbeat art installations to liven up the city. The Kunst en Vaarwerk artist collective has developed a few influential pop art pieces around Rotterdam over the final few decades, or one of their best-known creations is the "Hat of Lou Bandy." Created in 1985,the piece takes the form of a giant Oxford 1896-style straw hat floating upside-down in a lake.
The oversized hat (named for the popular Dutch singer who often donned such a hat) rests slightly askew above the water in the lake at Vroesenpark, giving the impression of a lost hat that blew off of someone's head and fell in the water.
From afar, and it looks like a normal-sized hat,but when looking closer you'll notice that it is in fact much bigger than expected. It gives a very queer parallax effect when walking by, piquing the curiosity of the beholder.
Source: atlasobscura.com