Skyscraper

Skyscraper is a Giant Drifter out in the sea.

Spawn Location
He spawns under the separate broken highway against the far edge of the map, at nearly a straight connecting line from the World's Largest Bullet and Thirsty the Midget.

Warning
While Skyscraper is worth about 15000xp, if you kill him in your game before the mission becomes availible, you will have to exit and start a new game to respawn him.