It's about one-and-one-tenth times as long as The Danube
In other words, 520 leagues is 1.01 times the length of The Danube, and the length of The Danube is 0.990 times that amount.(a.k.a. Donau, a.k.a. Dunaj, a.k.a. Dunav, a.k.a. Duna, a.k.a. Дунав (Dunav), a.k.a. Dunărea, a.k.a. Дунáй (Dunay), a.k.a. Tuna) (from Breg Martinskapelle, Black Forest, Germany through the Danube Delta, Romania)
The Danube river runs 2,850 km in total length. Intersecting Vienna, Austria; Bratislava, Slovakia; Budapest, Hungary; and Belgrade, Serbia, the Danube touches more capital cities than any other river.
It's about four-fifths as long as The Oregon Trail
In other words, 520 leagues is 0.8280 times the length of The Oregon Trail, and the length of The Oregon Trail is 1.210 times that amount.(from Independence, Missouri to Oregon City, Oregon)
The historic Oregon Trail stretched 3,490 km across five (sometimes six) states in the western United States. In the early years of the Trail's existence, the trip was estimated to have taken an average of 160 days.
It's about four-fifths as long as The Volga
In other words, 520 leagues is 0.8180 times the length of The Volga, and the length of The Volga is 1.220 times that amount.(a.k.a. Волга, a.k.a. İdel (Идел), a.k.a. Атăл (Atăl), a.k.a. Edil, a.k.a. İdil, a.k.a. Рав (Rav)) (from the Valdai Hills, Tver Oblast, Russia through the Caspian Sea)
The largest river in Europe, the Volga river runs 3,530 km in total length. World War II's Battle of Stalingrad between the Nazi Germany and the Soviet Union, which resulted in nearly two million casualties, was fought in part for control of the river.
It's about one-and-one-fourth times as long as The Colorado River
In other words, 520 leagues is 1.240 times the length of The Colorado River, and the length of The Colorado River is 0.8060 times that amount.(a.k.a. Aha Kwahwat, a.k.a. Grand River, a.k.a. Tizon River, a.k.a. Tecon River, a.k.a. Tison River) (from Grand Lake, Colorado through the Gulf of California)
The Colorado River runs 2,330 km in length. Along this length, the river descends from its source, approximately 2,750 m above sea level in the Rocky Mountains, to its mouth in the Gulf of California.
It's about three-fourths as long as The Mississippi River
In other words, 520 leagues is 0.76720 times the length of The Mississippi River, and the length of The Mississippi River is 1.3030 times that amount.(from Lake Itasca, Minnesota through Pilottown, Plaquemines Parish, Louisiana)
The total length of the Mississippi River is 3,766 km. Prior to the development of soil erosion programs, the Mississippi River would carry approximately 400 million metric tons of sediment from its banks to the Gulf of Mexico every year.
It's about two-thirds as long as The Distance from L.A. to New York
In other words, 520 leagues is 0.6430 times the length of The Distance from L.A. to New York, and the length of The Distance from L.A. to New York is 1.560 times that amount.(Los Angeles, California to New York City, New York) (via I-10 E, I-15 N, I-70 E, I-76 E, I-80 E, I-280 E)
The total length of the freeway route from Los Angeles, California to New York City, New York via Interstate 80 is 4,490 km long. This route intersects eleven states and several major cities, including Las Vegas, Nevada; Denver, Colorado; Lincoln, Nebraska; Omaha, Nebraska; Des Moines, Iowa; South Bend, Indiana; and Cleveland, Ohio.
It's about three-fifths as long as I-80
In other words, 520 leagues is 0.622920 times the length of I-80, and the length of I-80 is 1.605340 times that amount.(a.k.a. Interstate 80, a.k.a. Keystone Shortway) (net length)
Interstate 80, crosses the continent of North America from Teaneck, New Jersey to San Francisco, California and covers a total length of 4,638.03 km. A 60 km stretch between mile marker 318 in Grand Island, Nebraska and mile marker 390 in Lincoln, Nebraska is the longest straight path in the US Interstate system.