The Sextant Tower was probably the highest climbable structure at Burning Man 2015, and one of my favorite installation. It was very well built by a metallurgist aerospace engineer. There was also a zip-line installed at the top of the tower, and a bar that could be access only by climbing 15 feet up that vertical ladder.
For more info, go to the Sextant camp website.
Photo taken at the Burning Man 2015 festival (Black Rock Desert, Nevada).