Though it usually goes unnoticed, the humble sidewalk curb is actually a pretty impressive feat of engineering. The paved edges need to be perfectly smooth and uniform, and often take an expert to perfect. Fortunately, there's a machine that does most of the heavy lifting. Curb rollers take wet, chunky concrete and smooth it into the familiar curb shape we all know and love. Take a look at the process above. 

[h/t: The Kid Should See This]