A Dutch artist has started making unsightly structures disappear though various optical techniques, creating a more beautiful--and way more interesting--looking city.Roeland Otten, a designer in Rotterdam, has come up with an ingenious way of hiding some of those ugly, functional buildings that litter city streets: Make them look like they’re not there. Taking a leaf out a survivalist’s handbook, he is painting, tiling, and wrapping small structures, so they are less visible to the naked eye--or at least, a little less of an eyesore.Otten got the idea when neighbors near where he lives in the old part of the city wanted to do something about