It's about two-fifths as tall as St. Paul's Cathedral
In other words, 68,500 milimeters is 0.3940 times the height of St. Paul's Cathedral, and the height of St. Paul's Cathedral is 2.540 times that amount.(London, England, United Kingdom)
St. Paul's Cathedral measures 174,000 milimeters 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 two-fifths as tall as The Space Needle
In other words, 68,500 milimeters is 0.3720 times the height of The Space Needle, and the height of The Space Needle is 2.690 times that amount.(Seattle, Washington) (to aircraft warning beacon at peak)
Built for a 1962 World's Fair, the Space Needle stands 184,000 milimeters 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 three-tenths as tall as The Golden Gate Bridge
In other words, 68,500 milimeters is 0.3020 times the height of The Golden Gate Bridge, and the height of The Golden Gate Bridge is 3.310 times that amount.(San Francisco, California and Marin County, California) (height above water)
The height of each tower of Golden Gate Bridge is 227,000 milimeters 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 three-and-a-half times as long as a Cricket Pitch
In other words, 68,500 milimeters is 3.405110 times the length of a Cricket Pitch, and the length of a Cricket Pitch is 0.2936760 times that amount.(per Marylebone Cricket Council / International Cricket Council Law #6)
The length of a cricket pitch, from one bowling crease to the other, is 20,116.80 milimeters. The wickets at either end of the pitch stand 720 mm tall including the bails.
It's about three-and-a-half times as long as a Bowling Lane
In other words, 68,500 milimeters is 3.57590 times the length of a Bowling Lane, and the length of a Bowling Lane is 0.279650 times that amount.(USBC specifications; tenpin; including pin deck)
According to the United States Bowling Congress specifications, a tenpin bowling lane should measure 19,156 milimeters. In a Professional Bowling Association game, the lane must be lubricated by about 25 ml (0.85 fl. oz) of oil.
It's about one-fourth as long as The QE2
In other words, 68,500 milimeters is 0.2330 times the length of The QE2, and the length of The QE2 is 4.290 times that amount.(a.k.a. RMS Queen Elizabeth 2)
The QE2 has a total length of 294,000 milimeters. During its voyaging lifetime from 1969 through 2008, it travelled more than 9,600,000,000,000 milimeters, the furthest cumulative distance by any ship in modern history.
It's about four-and-a-half times as tall as The Hollywood Sign
In other words, the height of The Hollywood Sign is 0.220 times 68,500 milimeters.(a.k.a. Hollywoodland Sign) (Mount Lee, Hollywood Hills, Santa Monica Mountains, California)
Each of the white letters in the Hollywood Sign measures 15,000 milimeters tall. Built as an advertisement in 1923, the sign was intended to stand for only eighteen months.