1. The longest or second-longest in North America, depending on how you count. (The Missouri River could be considered longer.) Referred to by Abraham Lincoln as 'the father of waters,' the Mississippi begins at Lake Itasca, Minnesota, and flows 2,340 miles to a vast delta on the Gulf of Mexico, forming portions of ten state borders and the world's third-largest drainage basin. The Mississippi picks up numerous major tributaries including the Illinois, Missouri, Ohio, Arkansas, and Red Rivers, and flows past numerous major cities, including Minneapolis, St. Louis, Memphis, and New Orleans.

2. The triangular Negev covers the southern half of Israel.

3. The principal river of the Iberian Peninsula. Rising in east-central Spain, it flows west for roughly 645 miles to the Atlantic, passing through Lisbon, Portugal on the way. The cities of Toledo and Santarém are on the Tagus, and hydroelectric dams on the river produce huge artificial lakes, including the Sea of Castile.

4. A shield volcano that is the most active of the five volcanoes on the Big Island of Hawaii. The name 'Kilauea' means 'spewing' or 'spreading' in the Hawaiian language. In Hawaiian mythology, the volcano is the home of the fire goddess Pele. The three primary craters of Kilauea are Halemaʻumaʻu Crater, Puʻu Crater, and Puʻu ʻOʻo Crater. In addition, part of the volcano is covered by the Kaʻu Desert, a plain of dried lava and volcanic ash. The Hawaiian Volcano Observatory is on the rim of Kilauea's caldera.

5. A stratovolcanic island in the Sunda Strait between the Indonesian islands of Sumatra and Java. Prior to its massive 1883 eruption, there were three separate volcanic peaks: Perboewatan (completely destroyed by the eruption), Rakata (extant), and Danan (almost completely destroyed). The 1883 eruption of Krakatoa killed more than 35,000 people and is believed to have produced the loudest sound ever. Krakatoa is one of the largest volcanoes in the Pacific Ring of Fire. The continued activity of Krakatoa formed a new island, Anak Krakatau (or 'Child of Krakatoa') in 1927.

6. Africa's largest and the world's second-largest freshwater lake by area, Lake Victoria lies along the Equator and is shared among Uganda, Kenya, and Tanzania. Located on a plateau between two rift valleys, its lone outlet is the Victoria Nile, a precursor of the White Nile. Named by the British explorer John Hanning Speke after Queen Victoria, the introduction of the predatory Nile perch in the 1950s has caused environmental degradation, sending many native cichlid species into extinction.

7. Rises in Syria from springs near Mount Hermon. It flows south to Lake Merom, through the Sea of Galilee, and into the Dead Sea, which is 1,300 feet below sea level. The river forms the nation of Jordan's boundary with the West Bank and northern Israel. In the New Testament, the river was the site of the baptism of Jesus by John the Baptist. In modern times, about 80% of its water is diverted for human use, a figure that has led to the shrinking of the Dead Sea and serious contention among bordering nations.

8. The Gobi, Asia's second-largest desert (after the Arabian Desert), is bounded on the north by the Altai Mountains. It is known for its role in the Silk Road trading route and the Nemegt Basin, where fossilized dinosaur eggs and human artifacts have been found.

9. Africa's third-largest lake by area and the southernmost of the Great Rift Valley lakes, it is wedged between the nations of Malawi, Tanzania, and Mozambique. Fed by the Ruhuhu River, its lone outlet is the Shire River, a tributary of the Zambezi. Lake Malawi contains hundreds of species of endemic fish, especially cichlids.

10. Chief river of Pakistan and the source of the name of India. It rises in Tibet and flows 1,800 miles to a delta on the Arabian Sea southeast of Karachi. The five major tributaries of the Indus — the Jhelum, Chenab, Ravi, Beas, and Sutlej Rivers — are the source of the name of the Punjab region, which is Persian for 'land of the five rivers.' The Indus is the cradle of the Indus Valley Civilization, one of the world's earliest urban areas, whose main cities were Mohenjo-Daro and Harappa.

11. The second-tallest mountain in Africa is Mount Kenya, which shares its name with the country in which it is located. British geographer and political theorist Halford Mackinder led the first group to ascend the peak, which bypassed the Darwin Glacier and proceeded up the Diamond Glacier. Like Kilimanjaro, it was formed by a now-dormant volcano, and, like Kilimanjaro, part of its notoriety rests on a book. Facing Mount Kenya, an anthropological study of the Kikuyu people by Jomo Kenyatta, was one of the first such texts by an African ethnographer to gain fame.

12. The longest river in Canada. Flowing 1,080 miles out of the Great Slave Lake, the river flows past Fort Providence and Fort Simpson in Canada's Northwest Territories, emptying into a vast delta on the Beaufort Sea. The Mackenzie is the largest river flowing into the Arctic Ocean from North America. The river was named for Scottish explorer Alexander Mackenzie, who crossed Canada to the Pacific ten years before Lewis and Clark.

13. The largest man-made lake (by area) in the world, Lake Volta was created by the construction of Ghana's Akosombo Dam across the Volta River in the 1960s. The lake covers the area where the Black Volta and White Volta rivers formerly converged. The Akosombo Dam can provide over a gigawatt of power, enough to supply nearby aluminum smelters utilizing the energy-intensive Hall-Héroult process and the needs of the rest of the country.

14. Formerly and often called Mount McKinley, Denali is the highest mountain in North America. It is in south-central Alaska, in Denali National Park. The West Buttress route is considered the best path to ascend Denali. Frederick Cook, a man notorious for having faked the discovery of the North Pole, is now believed to have also faked his ascent of the mountain in 1906 as well, leaving a climbing party seven years later with the honor.

15. A stratovolcano in the Zambales Mountains on the eastern coast of the island of Luzon in the Philippines. In the aftermath of its 1991 eruption, the global temperature briefly decreased by almost a full degree Fahrenheit due to the ejection of aerosols and sulfuric acid. That eruption was ten times more powerful than the 1980 eruption of Mount Saint Helens; it killed at least 800 people and forced the evacuation of some 20,000 people. In its aftermath, monsoon rains created Lake Pinatubo in the resulting crater. In 2010, the indigenous Aeta people were formally granted domain over the volcano.

16. The most significant river of the southwestern United States. Beginning in Rocky Mountain National Park in Colorado, the Colorado River runs southwest for 1,450 miles to the Gulf of California in northwestern Mexico. The Colorado formed numerous canyons along much of its length, most notably the Grand Canyon in Arizona. The Colorado also has significant dams, including Hoover Dam near Las Vegas (forming Lake Mead) and Glen Canyon Dam in Arizona (forming Lake Powell).

17. The Painted Desert, which is shared by Grand Canyon and Petrified Forest National Parks, is known for its colorful, banded rock formations.

18. Its name means 'Empty Quarter' in English, and it is sometimes considered the most inhospitable place on earth. It is known for the world's largest oil field, the Ghawar, and for once being part of the frankincense trade.

19. Major river of the southern Great Plains. The Red River forms most of the border between Oklahoma and Texas along its 1,360-mile length. That border formed part of the border between Mexico (and later the Republic of Texas) and the United States after the 1819 Adams-Onís Treaty. The Red runs through the Louisiana cities Shreveport and Alexandria before emptying into the Mississippi south of Natchez, Mississippi.

20. Has formed the border between Texas and four Mexican states since 1848. It flows south out of Colorado through New Mexico before reaching the international boundary near El Paso. Texas's Big Bend National Park is named for the sweeping curve the Rio Grande cuts through the Sierra Madre Oriental. After leaving the mountains, the river flows past Laredo and Brownsville before it empties into the Gulf of Mexico.

21. Italy's longest river at 405 miles, it passes through Piedmont and Lombardy before entering the Adriatic 30 miles south of Venice. It flows through Turin and Cremona, and it passes near Milan, Padua, Pavia, and Mantua. The river has a long history of floods, and the man-made levees called argini which protect towns and crops can exacerbate the floods. Pollution, especially from Milan, is becoming a major environmental concern.

22. The Namib, a coastal desert, is known for its bizarre Welwitschia and medicinal Hoodia plants. It is thought to be the oldest desert in the world.

23. At 230 miles, the Shannon is Ireland's longest river. It flows from Lough Allen, and Loughs Ree and Derg are also on its course. At Limerick, the river widens into its namesake estuary and runs for 50 more miles before it enters the Atlantic. Peat bogs and marshes line the river for much of its course, and the Shannon is considered a dividing line between Ireland's more cultivated east and wild west. A chief tributary is the Suck River. The Shannon does not pass through Dublin, although the Liffey does.

24. A stratovolcano in the Cascades of Washington state. It is about 100 miles south of Seattle and about 50 miles north of Portland. It last erupted in May 1980, killing 57 people in the most devastating volcanic eruption in U.S. history. Perhaps the most famous casualty of that eruption was an innkeeper named Harry Truman (no relation to the president of the same name) who refused to evacuate from the mountain. Because of an avalanche of volcanic debris during that eruption, Mount Saint Helens lost about 1300 feet in height; lahars (mudflows of pyroclastic material) reached all the way to the Columbia River. The volcano is surrounded by Gifford Pinchot National Forest.

25. A stratovolcano on the Gulf of Naples in Campania in south-central Italy. Mount Vesuvius, which last erupted in 1944, is the only active volcano on mainland Europe. The most notable eruption of Mount Vesuvius was in AD 79 when it buried the Roman cities of Pompeii, Herculaneum, and Stabiae. The only surviving eyewitness accounts of that eruption are a pair of letters written by Pliny the Younger to Tacitus. The 1908 Summer Olympics were relocated from Rome to London after a surprise eruption of Mount Vesuvius.