There are now more than 1,000 sites to visit all over the world.
Not bad, considering the original list, compiled in 1978, included only 12 entries.
There are still a few months till the newest members of the prestigious list are announced in June, so here's a look back at 20 of the most beautiful -- and famous -- already on the list.
Site details in the gallery above, while info on getting to each is below.
The site is a 20-minute tuk-tuk ride from the city of Siem Reap.
The bulk of visitors come between November and February, when the weather is dry and temperatures are coolest (25-30 C).
To make the most of your visit to this incredible temple complex, a guide is essential.
We recommend Tong Hann of the Anantara Angkor Resort & Spa
His knowledge and respect for the sites and their history is phenomenal; he's particularly skilled at creating an itinerary that will keep you away from crowds and allow you to check out some lesser known but beautiful ruins.
It's possible to take a tour to the site, or simply wander in from Athens on foot.
The route along Adrianou Street to the back entrance of the site is a gentler climb than the Dionysus Theatre entrance.
For more information, visit the Greece tourism website
Ok, so it's still on the tentative list
But we couldn't help but include this beautiful stretch of ruins on the Irawaddy River that dates to the 10th century.
Located in Myanmar's central west, Bagan is serviced by flights, buses and trains from Yangon.
Accommodation is centered in the surrounding villages of New Bagan and Nyaung Oo.
Tours are available with Backyard Travel
, among others.
Galapagos Islands (Ecuador)
Located nearly 1,000 kilometers from mainland Ecuador, the islands are serviced by flights from Quito and Guayaquil.
Multi-day boat cruises are generally the best way to explore the islands.
For a truly rewarding experience, there's the National Geographic Galapagos Expedition
Goreme National Park and the Rock Sites of Cappadocia (Turkey)
Due to the remote nature of the site in central Anatolia, most visitors opt to fly in from Istanbul to visit the area on a tour.
Hotels cut out of the rock provide accommodation.
For more information, visit the Turkey tourism website
Great Barrier Reef (Australia)
Larger islands are serviced by flights from mainland Australia.
It's also possible to visit the reef via day trips from northern Queensland ports including Cairns and Port Douglas.
Hampi is serviced by overnight bus from Goa.
Trains run to nearby Hospet from Chennai, Mumbai, Bangalore, Delhi and Kolkata, and visitors will find a good range of low- to mid-range lodgings around Hampi village.
Tours available through On The Go Tours
, among others.
Iguazu National Park (Brazil and Argentina)
The less developed but refreshingly uncrowded Brazilian side of the falls is a half-hour bus ride from the city of Foz do Iguacu.
It's the same distance to the falls from Puerto Iguazu on the Argentine side.
The two countries are connected via a bridge downriver of the falls.
For more information, visit the Argentina tourism website
Los Glaciares National Park (Argentina)
Most visitors to this remote southern region of Argentina base themselves in El Calafate, the closest town to the park entrance.
There are daily flights and buses from the capital, Buenos Aires.
For excursion options, check out Gigantes Patagones
Machu Picchu (Peru)
Several multi-day treks terminate at Machu Picchu, but it's also possible to take a train from Cusco to Aguas Calientes, and climb a steep flight of stairs or bus up to the site.
Only the first 400 daily visitors are granted entry to Wayna Picchu, a separate set of ruins overlooking the main complex.
offers a range of tour options.
Mont-Saint-Michel is serviced by buses/tours from Rennes and St-Malo, but it's also possible to stay in one of Mont Saint-Michel's small hotels.
For more information, visit the Normandy tourism website
Buses and day/overnight tours run from Jordan's capital Amman and the port city of Aqaba.
It's also possible to organize tours from Egypt, and the Israeli resort town of Eilat.
For longer stays, you can bunk down in Wadi Musa, Petra's neighboring town.
For more information, visit the Jordan tourism website
Pyramids of Giza (Egypt)
Just 25 kilometers southwest of Cairo along the Nile River, the complex is most easily visited on a day trip from Egypt's capital.
For more information, visit the Egypt tourism website
Rapa Nui (Chile)
While it's possible to access Easter Island by air from Tahiti, most visitors opt for the five-and-a-half hour flight from Santiago, Chile.
For more information, visit the Chile tourism website
Serengeti National Park (Tanzania)
The short October/November and March/April rainy seasons notwithstanding, the Serengeti, usually accessed via Kilimanjaro or Nairobi airports, offers great game viewing year-round.
Sigiriya (Sri Lanka)
The central Sri Lankan site is located two to three hours by local bus from the city of Kandy (via Dambulla, home to a massive cave temple complex).
It's also possible to organize a tour or personal driver from Kandy.
For more information, visit the Sri Lanka tourism website
Located a few minutes drive from the small Yucatan Peninsula township of Tulum, the easily accessible ruins lie about 60 kilometers south of the larger township of Playa del Carmen, and a further 60 kilometers from Cancun.
For more information, visit the Mexico tourism website
Just south of Sicily, Malta is connected by flights from across Europe.
It's possible to stay in Valletta, but the bulk of visitors make for the tiny nation's beach resorts.
For more information, visit the Malta tourism website
Venice and its lagoon (Italy)
Venice is served by nearby Marco Polo and Treviso airports, while trains arrive at the Venezia Santa Lucia train station in the western part of the city.
For more information, visit the Italy tourism website
Yellowstone National Park (United States)
Located around 100 kilometers from Jackson Hole, Wyoming, the closest major airport hub, the park has five main access points.
Most visitors choose to drive throughout the park, camping en route.
For more information, visit the Wyoming tourism website
Published December 2013, updated February 2015.