Including fantasy structures as part of "LEGO skylines" may be a bit of a stretch but J.R.R. Tolkien seemed to have a "thing" about towers. He scattered mentions of a dozen or more towers throughout the Lord of the Rings and the Silmarillion. Some of these were destroyed but others lasted for a thousand years or more. The heights of the towers were generally not mentioned with two exceptions and both of these would meet the current definition of skyscrapers (500 feet or higher) assuming they were contiguously habitable structures from top to bottom.
The roof of the Tower of Orthanc was specific mentioned as being 500 feet above Isengard.
Here is my 7.9 foot high more or less minifig scale LEGO version of Orthanc:
Photo credit:
me / flickr
The other tower, Barad-dur, Middle Earth's only Supertall at an estimated 3,000 or more feet tall, was built by Sauron and when he was vanquished the tower went with him.