In our roundup of travel news this week: the secret tunnel city underneath Rome, China’s “8D city” where trains pass through walls, plus a new report reveals the world’s busiest flight routes, biggest aviation markets and most popular planes.

Isn’t data just delicious?

The International Air Transport Association (IATA) has released its 2024 World Air Transport Statistics report, and it’s filled with fascinating nuggets.

Here are a few to wow your avgeek friends.

The United States is the world’s biggest aviation market, with 876 million passengers per year in 2024, mostly flying domestic. That’s four times more than India, which is the world’s most populous nation and the fifth biggest aviation market.

China is hot on the States’ heels at No. 2, however, with 741 million passengers in 2024 and a whopping 18.7% growth year-on-year, compared to America’s modest 5.2%.

The United Kingdom is but a 94,000-square-mile island nation, but it’s the world’s No.3 aviation market, with 261 million passengers scooting above land and sea in 2024.

A lot of those Brits will have been heading to vacation hot spot Spain, which is the No. 4 aviation market, with 241 million passengers last year.

Busiest flight routes and most popular planes
Let’s continue with more tidbits from the IATA report.

Nine out of 10 of the world’s busiest flight routes are in the Asia-Pacific region. However, the world’s No.1 is a South Korean domestic flight: the 1 hour and 15 minute trip between the island resort city of Jeju (CJU) and the capital, Seoul (GMP). More than 13 million passengers flew the route in 2024.

The busiest route in North America is an airport pairing as classic as ketchup and hot dog. It’s JFK to LAX (or New York to Los Angeles, as if you didn’t know), and 2.2 million passengers made the voyage last year.

The most popular European route is the hour-long flight between Spanish vacation hot spots Barcelona (BCN) and Palma de Mallorca (PMI), with 2 million passengers in 2024. Want a less busy flight? Take a look at our guide to the parts of Spain that aren’t sick of tourists.

The busiest route in Latin America (with 3.8 million passengers) is the one-hour flight between Bogotá (BOG), the Colombian capital, and Medellín (MDE), Colombia’s second-largest city.

Africa’s most popular route, with 3.3 million passengers, is the two-hour domestic South African flight between Cape Town (CPT) and Johannesburg (JNB).

Finally, while the Boeing 737 Max has had a calamitous history, the Boeing 737 (including all variants), remains the world’s most-used aircraft, making 10 million flights in 2024.

The No. 2 and No. 3 planes are also narrowbody aircraft, made by Boeing’s European rival Airbus. The A320 flew 7.9 million flights and the A321 flew 3.4 million.

Enough about the journeys, let’s talk destinations. Here are three to consider for your next big trip.

Halfeti, in southeastern Turkey, was one of several towns and cities to be intentionally flooded when the Birecik Dam was built in 2000. But residents still live in the half-submerged town — while dark roses grow in the mineral-rich lands.

Angola, in southern Africa, is twice the size of Texas and boasts spectacular natural wonders that few tourists have seen. After decades largely cut off from the world, the country is opening up, infrastructure is improving, and discovery awaits.

Chongqing, in a mountainous area of southwestern China, is attracting younger travelers thanks to its mindbending, Instagram-friendly terrain that’s so multilayered some are calling it the country’s “8D city.” To see what we mean, check out this train passing right through a residential building.

A network of ancient caves and tunnels lies some 75 feet under the city of Rome, hidden from the world for more than a century. Now this subterranean labyrinth is being uncovered once more. Here’s what 21st-century visitors can see.

One of a cave explorer’s most essential items is, of course, a headlamp. Our partners at CNN Underscored a product reviews and recommendations guide owned by CNN, have this guide to the best headlamps for 2025.