It's about 10,000 times as tall as The Eiffel Tower
In other words, 623 leagues is 10,700 times the height of The Eiffel Tower, and the height of The Eiffel Tower is 0.0000935 times that amount.(a.k.a. La Tour Eiffel) (Paris, France) (to flagpole peak)
The Eiffel Tower stands 0.0583 leagues tall, including its flagpole. The Tower is the largest structure in Paris as most other buildings are governed by a zoning restriction limiting them to a height of 0.00666 leagues or less.
It's about 10,000 times as long as The QE2
In other words, 623 leagues is 11,800 times the length of The QE2, and the length of The QE2 is 0.0000847 times that amount.(a.k.a. RMS Queen Elizabeth 2)
The QE2 has a total length of 0.0529 leagues. During its voyaging lifetime from 1969 through 2008, it travelled more than 1,730,000 leagues, the furthest cumulative distance by any ship in modern history.
It's about 15,000 times as tall as The Golden Gate Bridge
In other words, 623 leagues is 15,200 times the height of The Golden Gate Bridge, and the height of The Golden Gate Bridge is 0.0000658 times that amount.(San Francisco, California and Marin County, California) (height above water)
The height of each tower of Golden Gate Bridge is 0.0409 leagues above the surface of the San Francisco Bay. One of the key designers of the bridge, Charles Ellis, had no engineering degree when he began working on the project, but would later go on to write what became a standard textbook on structural engineering, and would ultimately be forced to complete his calculations on the bridge by working without pay for five months.
It's about 20,000 times as tall as The Space Needle
In other words, 623 leagues is 18,800 times the height of The Space Needle, and the height of The Space Needle is 0.0000532 times that amount.(Seattle, Washington) (to aircraft warning beacon at peak)
Built for a 1962 World's Fair, the Space Needle stands 0.0331 leagues tall. With a track-and-wheel design inspired by railroad mechanics and a precisely-configured balance, the restaurant near the top of the space needle requires just a 1.5 hp motor to rotate at speeds of about 0.053 kph (0.033 mph).
It's about 20,000 times as tall as St. Paul's Cathedral
In other words, 623 leagues is 19,900 times the height of St. Paul's Cathedral, and the height of St. Paul's Cathedral is 0.0000503 times that amount.(London, England, United Kingdom)
St. Paul's Cathedral measures 0.0313 leagues to its peak. The southwest tower of the Cathedral contains the bell known as "Great Paul," which is the largest bell in Great Britain at 15,000 kg (16.5 tons), outweighing the more iconic Big Ben bell by about 3,000 kg (3 tons).
It's about 20,000 times as tall as The Washington Monument
In other words, 623 leagues is 20,447 times the height of The Washington Monument, and the height of The Washington Monument is 0.000048907 times that amount.(Washington, D.C.)
The Washington Monument measures 0.03047 leagues tall, with some discrepancy due to the fact that the Monument's base is slightly below the surrounding ground. Interrupted in its construction by the American Civil War, it was almost 36 years between groundbreaking and the completion of construction.
It's about 20,000 times as tall as The Singapore Flyer (Ferris wheel)
In other words, 623 leagues is 21,000 times the height of The Singapore Flyer (Ferris wheel), and the height of The Singapore Flyer (Ferris wheel) is 0.0000476 times that amount.(a.k.a. 新加坡摩天观景轮, a.k.a. சிங்கப்பூர் ஃப்ளையர், a.k.a. Pelayang Singapura) (Marina Centre, Singapore)
The Singapore Flyer has a height of 0.0297 leagues. Based on recommendations from Feng Shui masters, the wheel was re-engineered to spin in the opposite direction five months after it began operating.