1. Afar, Ethiopia
The Afar region, a low-lying spot in northern Ethiopia, is home to two important anthropological discoveries: the famous hominid fossil Lucy and the world’s oldest stone tools. But it has several other distinctive features. Located near the meeting point of three tectonic plates (the African, Arabian, and Indian plates), the area is seismically active, with near-continuous earthquakes that can split the earth’s crust, opening long rifts. According to recent reports, a large fissure has appeared in Afar that will eventually separate the Horn of Africa from the rest of the continent. There are also volcanoes. Rising from below sea level, Erta Ale, the most active volcano in Ethiopia, erupted several times in 2005, reportedly displacing about 50,000 nomads. The Afar depression happens to be one of the hottest inhabited places on earth, especially from May to August, when temperatures can reach a dangerous 113 degrees Fahrenheit.

The challenging part: Because of the possibility of land mines, abductions, and banditry, the U.S. State Department reports that “travel in the Afar region towards the Eritrean border is generally discouraged and permitted to Embassy personnel only on a case-by-case basis.”

2. Mothra Field, Pacific Ocean
Named after the infamous giant-insect monster of Japanese horror films, the Mothra Field is even more astonishing than its cinematic namesake. Discovered in 1996, this biological hot spot is composed of a series of hydrothermal vents that dot a volcanic ridge some 200 miles off the coast of Washington State. A mile beneath the sea surface, 60-foot pinnacles called black smokers puff out superhot fluids (about 600 degrees Fahrenheit). Despite the heat, a variety of colorful organisms manage to thrive nearby, including one—discovered in 2003 and provisionally named Strain 121—that can withstand a temperature of 250 degrees. Extreme environments like these may have been the birthplace of life on earth.

The challenging part: Marine biologists are able to explore the Mothra Field in submersibles, but an expedition requires funding and years of planning.

3. “Extinct” Bird Hunt, southern United States
It was a shocking moment in the birding world when a kayaker in the Cache River National Wildlife Refuge in Arkansas reported spotting a bird that fit the description of an ivory-billed woodpecker in 2004. That magnificent bird had not been seen for 60 years and was believed to be extinct. The Cornell Lab of Ornithology, the Nature Conservancy, and others launched a search for the woodpecker that continues to this day. After countless outings with teams of ornithologists and large groups of volunteer birders, they have reported glimpses of the ivorybill, analyzed a short video of it in flight, and recorded a double knock that might have come from the rare bird. Between November 2006 and April 2007, searchers logged 24 possible encounters with the woodpecker.

The challenging part: Although it takes only basic canoeing and hiking smarts to traverse the ivory-billed woodpecker’s traditional territory—the old woods and swamps of Arkansas, Texas, Louisiana, Mississippi, Alabama, Florida, and South Carolina—the odds are remote that you will actually see this lauded bird.

4. Mammalogy Tour, New York City
The Behind the Scenes Tour of the Department of Mammalogy at the American Museum of Natural History ushers you into the world of scientists who spend their days studying dead animals. Highlights include a look at preserved animal specimens that zoologists and other scientists are still analyzing and a visit to the department’s room-size walk-in freezer, where everything from new items for an upcoming exhibition to elephant skins are kept. You might even see a large mammal, like a fully mounted mountain lion in standing position. “We put specimens in the freezer to kill any insects that might be on them,” explains Neil Duncan, collections specialist for the museum’s Department of Vertebrate Zoology. Duncan oversees another strange site in the tour: the room where dermestid beetles nibble tiny bits of flesh left on the bones of fish, mammals, and birds.

The challenging part: The museum offers this tour periodically, to members only. The two dozen or so slots go quickly, so watch for the tour’s posting in the members’ newsletter or the members section of the museum’s website. Because specimens move in and out of the giant freezer regularly, what will be in it for any given tour is a matter of chance. (However, the beetles are almost always active.) Warning—the odors can be intense.

5. Trinity Site, White Sands Missile Range, New Mexico
What does it feel like to stand at the spot where the nuclear age began? You can get some idea by visiting Trinity Site, where the first explosion of an atomic bomb occurred on July 16, 1945. The detonation unleashed the colossally destructive power of a fission chain reaction and changed the world forever. A plaque marks the explosion site, and a museum documents the life and culture of the Manhattan Project bomb builders.

The challenging part: Located in the sparsely settled desert of southern New Mexico, the site is open to visitors only twice a year (on the first Saturdays of April and October), though the museum is open year-round.