Tower cranes are a common fixture at any major construction site. They're pretty hard to miss -- they often rise hundreds of feet into the air, and can reach out just as far. These huge machines used to be built up by human crews, but with new technology and automation those days are almost over.
Today many tower cranes can build themselves up. There is still a crew needed to assemble the jib and the machinery section, but once all parts are in place a crane can add one mast section at a time to grow itself up with the help of the crane operator.
Here is the animated version of the process that shows more details.