Skyscraper Day is a time to celebrate one of the most influential inventions in human history. Tall multi-story buildings have enabled people to live more closely together, saving land from development, and turning cities into artificial mountain ranges, each with its own distinct look.
Dwellings of many floor levels have existed at least since medieval times, in places like Yemen and central Europe, but it was not until the mid-nineteenth century that technology enabled buildings to rise higher and higher. Two developments in particular made this possible: the elevator, and the skeletal frame. New York and Chicago were the original laboratories for skyscraper technology, as the masonry frame was replaced by lighter and stronger skyscraper skeletons, first of steel then of concrete.
The 3rd of September was chosen for Skyscraper Day to commemorate the first master architect of high-rise buildings, Louis Sullivan, who was born in Boston on 3 September 1856. Sullivan worked in Chicago with William LeBaron Jenney, engineer of the first steel-framed 10-story building, the now-demolished Home Insurance Building. Sullivan created his own uniquely American brand of Art Nouveau. His buildings achieved a rare elegance, combining simple forms with elaborate organic ornamentation, following his famous principle that "Form follows function". Sullivan was the revered mentor of Frank Lloyd Wright, widely considered the greatest architect of the 20th century.
Skyscraper Day is an occasion to explore, photograph, discuss, and admire tall buildings. An architectural tour is an excellent way to celebrate; many cities offer popular tours, or you could lead one yourself. You can also join an online building-related community to talk about new developments or to contribute data and photos from your city or your travels. Follow us on Instagram or Twitter: @skyscraper_day 
You will find more information about tall buildings in these great online resources: Wikipedia Rich source of information on significant tall buildings, with several skyscraper-related lists https://en.wikipedia.org/wiki/Main_Page CTBUH (Council on Tall Buildings and Urban Habitat) Professional organization of engineers, architects, and construction companies involved in skyscrapers https://www.ctbuh.org
DATABASES
SKYDB A database of skyscrapers and other tall buildings for 10,000+ cities worldwide https://www.skydb.net
SkyscraperPage A community of tall buildings fans with diagrams and a discussion forum http://skyscraperpage.com/cities/
The Skyscraper Center A database of the world's tallest skyscrapers http://www.skyscrapercenter.com/
Structurae Database of buildings and major structures with a focus on engineering http://en.structurae.de/
FORUMS
Skyscraperpage Forum Discussion forum about skyscrapers and new construction, primarily in North America http://skyscraperpage.com/forum/ Skyscrapercity International forum about skyscraper development with many active subforums https://www.skyscrapercity.com/forums/
OTHER RESOURCES
Skyscraper Museum A museum in downtown New York City dedicated to skyscrapers, with rotating and permanent exhibits https://skyscraper.org
IHP International Highrise Award An architectural award chosing the best skyscrapers worldwide every two years https://international-highrise-award.com
ARCHITECTURE with sauce A website offerings tinker sets of world-famous skyscrapers for free downloading https://www.craftingmodels.com