Solar flares and explosions hurl particles that collide with the Earth's atmosphere, producing energy emitted as photons, or light particles. It takes 100 million photons to make the aurora borealis, or northern lights, visible to the naked eye.
As with rainbow spotting, there are no guarantees. The key ingredients are a cloudless sky, little or no moon, and luck. For the best odds, head near or above the Arctic Circle from October through March. At 78 degrees north, between mainland Norway and the North Pole, Spitsbergen on the Svalbard archipelago is the world's northernmost place reached by regularly scheduled flights (about $200 round trip from Olso). If that's too hardcore, go as far north as you can manage. The Norwegian town of Hammerfest was popularized as a viewing place by Bill Bryson's Neither Here Nor There; Tromsø is a decent-size city with charm 250 miles north of the Arctic Circle. Both cities are stops on the slow-moving Norwegian Coastal Voyage cruise (800/323-7436, coastalvoyage.com, six-night packages from $1,067). Though 110 miles south of the Arctic Circle, Fairbanks, Alaska, has reliable enough viewing to attract scientists annually; flights from Seattle cost around $500 in winter.
You made it
It helps if your destination offers more than the lights, because sitting around in the freezing dark can try the most patient of souls (and in winter, the farther north you go, the less daylight you get). Svalbard is ideal for snowmobiling, dogsledding, and polar-bear viewing. Basecamp Spitsbergen arranges tours, as well as accommodations aboard an old ship embedded in ice or in a trappers' lodge (011-47/7902-4600, basecampexplorer.com, doubles from $165). Many decent Fairbanks motels charge under $100 a night; drive a few miles away from the city in any direction for a chance at clear viewings. Or stay outside town at Northern Sky Lodge, a log B&B with dogsledding tours (907/388-9954, northernskylodge.com, doubles from $75), or Mt. Aurora Fairbanks Creek Lodge, with 270 degrees of sky visible from its deck (907/389-2000, mt-aurora.com, $289 for two with meals). Whichever destination you choose, ask around about when to head out for a look; locals keep tabs on the best viewing times, which can change seasonally.
Every 11 or so years, the northern lights are known to appear way below the Arctic Circle. In 2000 they were visible in El Paso, Tex. Wherever you are during the winters of 2011 and 2012, be sure to look up at night.
The Blue Hole, Belize
Once a dry cave system, the Blue Hole was formed after the last ice age, when the Caribbean Sea engulfed the entire area and the cave's roof collapsed. The resulting sinkhole is more than 400 feet deep, 1,000 feet in diameter--and a mainstay on divers' wish lists. Getting there Fly 20 minutes from Belize City to San Pedro, the only real town on the resort island of Ambergris Cay, for about $110 round trip via Tropic Air (800/422-3435, tropicair.com) or Maya Island Air (800/225-6732, mayaairways.com). Or hop a ferry: Caye Caulker Water Taxis charge $16 each way for the 75-minute trip from Belize City (cayecaulkerwatertaxi.com, 011-501/226-2194). Most places to stay are huddled around San Pedro; scout options at ambergriscaye.com. For something more removed, try the Salamander Hideaway (011-501/209-5005, salamanderbelize.com, cabanas from $130), a quiet, solar-powered resort north of town reached by a half-hour boat ride ($25 round trip). Many agencies, including regional specialist Capricorn Leisure Corp., sell air-hotel packages to Ambergris Cay (800/426-6544, capricorn.net). Ambergris Divers (011-501/226-2634, ambergrisdivers.com) and Amigos del Mar (011-501/226-2706) offer Blue Hole day trips, departing at 5:30 a.m., returning at 5 p.m., with two hours' travel each way, for $185 plus $40 for park fees. If that's not enough time in the water, consider a live-aboard boat such as Peter Hughes Diving's Sun Dancer II: A seven-night package with meals, space for 20 passengers, and up to five dives per day starts at $1,895, plus fees of about $200 (305/669-9391, peterhughes.com). You made it Due to limited sunlight and water circulation in the Hole, its limestone walls don't support all that much marine life and are rather sterile and rocky. Still, while descending, look toward the walls rather than into the hypnotizing, deep blue of the Hole's center, as the low light and lack of visual cues can be disorienting. In a cavern about 100 feet down, huge stalactites hang from the ceiling. Some are 40 feet long and more than 10 feet wide; feel free to slalom through. Most groups don't go lower than 130 feet, the maximum depth for recreational dives. Several kinds of sharks (reef, blacktip, bull, hammerhead) may appear, adding to the excitement. Attacks are extremely rare. Who knew? For generations, people believed the Blue Hole was bottomless. But in 1970 that notion was put to rest by Jacques Cousteau. Using a minisub, the famous explorer reached the bottom, at a depth of around 415 feet.
Machu Picchu, Peru
'Machu Picchu might prove to be the largest and most important ruin discovered in South America since the days of the Spanish conquest,' wrote Hiram Bingham, the explorer who stumbled upon the marvelous granite city in 1911. Bingham was understating things: Every year, half a million tourists head to a remote Peruvian ridge to visit the 15th-century ruins. Getting there Round-trip flights between Miami and Cuzco, the launching point for visits to Machu Picchu, start at $550 on LAN Airlines (connecting via Lima). Three types of trains make the four-hour journey from Cuzco to Aguas Calientes, an ATM-less town at the base of Machu Picchu: the Backpacker ($68 round trip), Vistadome ($105), and Hiram Bingham ($495). The main difference between the first two is that the Vistadome has more windows. Hiram Bingham service comes with afternoon tea and a four-course meal accompanied by musicians. Reservations are required for all (perurail.com). Consider spending a night in Aguas Calientes, which allows more time for poking around the ruins. One package, from Cuzco-based SAS Travel, includes a round trip on the Vistadome, one night near the ruins at the Pueblo Hotel, and a guided tour from $175 (011-51/8425-5205, sastravelperu.com). Outfitters also lead several-day hikes to Machu Picchu. The traditional Inca Trail, part of the empire's original network of stone footpaths, has grown so popular that the government caps the number of hikers at 500 a day and requires that all tourists go with a licensed guide. Prices for the four-day trek from operators such as Peru Treks & Adventure (perutreks.com) start at $295 and include food, entrance fees, porters, and all camping equipment except your backpack and sleeping bag. The dry season (May-September) is best for hiking and exploring, though it's also crowded. Far fewer people come in the wet season, but you run the risk of getting stuck in Aguas Calientes; mudslides sometimes block train tracks for days. You made it Starting at 5:30 a.m. in Aguas Calientes, buses leave as soon as they fill, bound for the ruins' gate 15 minutes away ($6 each way). Alternately, a stone staircase to the gate takes about an hour to climb and 45 minutes to descend. To avoid lines at the gate, buy admission tickets in Cuzco or Aguas Calientes (inc-cusco.gob.pe, $23). From the entrance, a path leads to a terrace for the postcard view, with the stone city laid out at the foot of a taller mountain, Huayna Picchu. Wooden signs indicate the important ruins, but there's little else in the way of explanatory information. Tour guides lingering at the entrance charge $15-$20 per person for a 20-minute tour, largely doling out the same basics that are in any guidebook. Who knew? Bingham thought that one group of stone chambers served as Machu Picchu's prison. More likely, the Inca used the spot for some kind of religious ceremonies. It's known as the Temple of the Condor because the layout resembles one of the huge birds considered sacred by the Inca.
Leaning Tower of Pisa
The tower started leaning shortly after construction began in 1173, and the tilt got worse as work on the building continued over two centuries, with several delays and attempts to correct the problem. Blame the marshy soil of coastal Tuscany. Getting there Most people make Pisa a day trip from Florence; it's an hour-long $6 train ride away (trenitalia.com). After leaving the main exit of Pisa Centrale station, stop at the tourist office on the left for a free town map. The tower is a half-hour walk north. Alternately, three buses, the Navetta A, #3, and #4, run approximately every 10 minutes (25¢) and drop off passengers in front of the Field of Miracles, a piazza that's home to the tower, as well as to the Duomo and the Baptistry (both of which also tilt, but less obviously). A taxi from the train station costs about $9. You made it An 11-year, $27-million restoration that removed soil beneath one side and shifted the top of the tower closer to vertical by 16 inches, or half a degree, was completed in 2001. Tickets to get inside are $18 and are good for pre-set 30-minute visits; only 30 people can enter at a time. In the summer, it's wise to reserve tickets at opapisa.it for an additional $2.40 per person. Pickup is right next door to the tower at the Opera Museum. Killing time while waiting for your time slot isn't difficult; souvenir stands sell leaning mugs, tower snow globes, and other kitsch. Waiting also gives you the opportunity to take the requisite watch-me-prop-up-the-tower photo. Most people pose behind the Duomo, on the southwestern side of the field, but a better spot is the northeastern corner, where there's less risk of someone stepping in the frame. Once inside the tower, ascending the off-kilter circular staircase feels somewhat like bobbing from side to side on wide waves. Guards are strict about the half-hour limit, so even if you climb the 294 steps fast, you'll still have only 20 minutes at the top to let your stomach settle and check out the view before they usher you back down. For an excellent postclimb lunch, head beyond the tower to Osteria dei Cavalieri, a Slow Food-approved restaurant with pastas for $13 (Via San Frediano 16, 011-39/050-58-08-58). Alternately, Divincibo, a shoebox-size store on the Piazza delle Vettovaglie, sells sandwiches for $4 (011-39/050-573-952). Royal Victoria Hotel is an elegant family-run establishment with a roof garden and large rooms (011-39/050-940-111, royalvictoria.it, from $94). Who knew? Children age 8 and up pay full admission. Kids under 8 aren't allowed inside the tower.
Volcanoes National Park in Hawaii
The Hawaiian Islands were formed millions of years ago by volcanoes beneath the Pacific, and the job still isn't done. Hawaii, or the Big Island, continues to grow thanks to Kilauea, the particularly active volcano on its southeastern shore. Around 600 acres of land have been added in the past two decades alone. Getting there The park entrance is two hours by car from the resort area of Kailua-Kona, and 45 minutes from the port town of Hilo. Both are served with flights from Honolulu; nonstops from Kona connect daily to the mainland. Park admission is $10 per carload, good for seven days (808/985-6000, nps.gov/havo). You made it Crater Rim Drive loops around the park's centerpiece: Kilauea Caldera, a crater nearly three miles across and 400 feet deep. A short walk off the road, the Halemaumau Overlook features the best views. Further along is a parking lot bordered on one side by the Thurston Lava Tube, a spooky tunnel that you can walk through, and on the other side by the Kilauea Iki Trail, which leads across a black lava lake that still emits steam. To see lava on the move, turn off the main loop onto Chain of Craters Road, a route that winds past black landscapes with "lava trees" (fingerlike, lava-covered trees) interspersed with rain forest, before ending at a ranger station. If rangers say it's OK, you can walk on gravel for a few hundred yards to where the road succumbed to lava flows in 2003. A marked trail continues over uneven mounds of hardened lava; a billowing plume of steam caused by lava hitting the water will be visible at the shoreline. The best lava shows are after dark. Even if you can't get close enough to see lava oozing, the sky will glow an eerie red. One flashlight per person is essential if you want to hike and see more. To increase your chances of spotting lava, take a guided, full-day hike to the latest flows from Arnott's Lodge and Hiking Adventures (808/969-7097, arnottslodge.com, $80). The lazy, all-but-guaranteed way to see lava is by hopping a helicopter ride from Hilo with Blue Hawaiian (800/745-2583, bluehawaiian.com, $210) or Sunshine Helicopters (800/469-3000, sunshinehelicopters.com, $202). Both give discounts for online bookings. Who knew? Jack Thompson is the only person still living in a neighborhood surrounded by lava fields on the park's east side. The curious can check out Thompson's Lava House and even stay over for $100 a night (808/937-4282). The hike to the house takes about an hour from the end of Hwy. 130.