It's about one-and-three-fifths times as tall as Olympus Mons
In other words, 42,000 meters is 1.6 times the height of Olympus Mons, and the height of Olympus Mons is 0.63 times that amount.(a.k.a. Mount Olympus) (Mars)
The tallest mountain in the solar system, Olympus Mons rises to approximately 27,000 meters. The mountain has been known to astronomers since the nineteenth century because it is tall enough to rise above Mars' frequent dust storms.
It's about half as long as The Panama Canal
In other words, 42,000 meters is 0.48 times the length of The Panama Canal, and the length of The Panama Canal is 2.1 times that amount.(Canal de Panamá) (Panama)
Connecting the Atlantic and Pacific Oceans across the Isthmus of Panama, the Canal measures 88,000 meters in length. Ships passing through the Canal are raised (and then lowered) 26 meters above sea level through the lock-and-dam system.
It's about two-fifths as wide as The English Channel
In other words, 42,000 meters is 0.393 times the width of The English Channel, and the width of The English Channel is 2.54 times that amount.(average width between Isle of Ushant and The Walde Lighthouse) (La Manche, Ärmelkanal, Mor Breizh, Mor Bretannek) (a.k.a. The Channel)
The English Channel measures between 107,000 meters, narrowing as it flows northeast. The world speed record for a Channel crossing by swimmer was set by Australian Trent Grimsey in 2012, with a time of 6 hours, 55 minutes.
It's about one-third as long as The 405
In other words, 42,000 meters is 0.36039 times the length of The 405, and the length of The 405 is 2.7748 times that amount.(a.k.a. I-405, Interstate 405, San DIego Freeway) (Southern California)
Running from Irvine to San Fernando, The 405 runs a total of 116,540 meters. The 405 is the most heavily-trafficed freeway in the United States, with an average speed as low as 8 kph during rush hours.
It's about one-third as long as Hadrian's Wall
In other words, 42,000 meters is 0.35 times the length of Hadrian's Wall, and the length of Hadrian's Wall is 2.9 times that amount.(a.k.a. Roman Wall, a.k.a. The Wall, a.k.a. Vallo di Adriano, a.k.a. Vallum Aelium, a.k.a. Severus' Wall) (from North Tyneside, Tyne and Wear, England, United Kingdom to Cumbria, North West England, United Kingdom)
Hadrian's Wall, which crossed England form the North Sea to the Irish Sea during the time of Roman rule, measures 120,000 meters (about 79 Roman miles). Roman soldiers — at one time up to 10,000 of them — only occupied Great Britain for about 246 years after the wall was built, after which time the local Brits began to take residence the wall's garrisons.
It's about four times as tall as Maxwell Montes
In other words, 42,000 meters is 3.8 times the height of Maxwell Montes, and the height of Maxwell Montes is 0.26 times that amount.(Ishtar Terra, Venus)
Maxwell Montes rises to a total height of 11,000 meters. Since Venus does not seem to have the kind of tectonic activity which gives rise to mountains on Earth, the origin of the Venusian mountain remains the subject of some dispute.
It's about four times as deep as The Challenger Deep (Marianas Trench)
In other words, 42,000 meters is 3.8525 times the depth of The Challenger Deep (Marianas Trench), and the depth of The Challenger Deep (Marianas Trench) is 0.25957 times that amount.(near Marianas Islands, a.k.a. Ladrones Islands, northwestern Pacific Ocean) (depth below sea level)
The Challenger Deep, at the southern end of the Marianas Trench, reaches a depth of 10,902 meters below sea level. The first manned expedition to the bottom of Challenger Deep took 4 hours and 48 minutes in 1960. This was the only manned descent to the floor of the Trench until 2012, when director James Cameron made the trip; several other descents have been made since then.