Here are some of my world highlights:

Waitomo Glowworm Caves - I recommend taking the longest possible tour with The Legendary Black Water Rafting Co..

Actun Tunichil Muknal - I've got a thing for caves, and this one is some serious adventure. I'd tell you more, but it would spoil the surprise.

Franz Josef Glacier - This is by far the best glacier tour I've been on. If you're one of those people who sees glaciers as big slabs of static ice, this will change your mind.

Besseggen - One of the world's great day hikes. You won't believe the scenery.

Landmannalaugar - This is another amazing hike. Volcanic landscapes, crazy colors, bizarre topography ... you won't believe this place.Hanoi - Great museums, amazing food, out-of-this-world people watching.

Oregon - All around, one of the most-overlooked places in the U.S., especially by foreign visitors who head straight to New York, LA, Chicago or (even worse) Las Vegas. Portland has great food, terrific scenery, some nice architecture and friendly, outgoing residents. Drive around toward the coast, too, and do some hiking and camping. I highly recommend Astoria.

Java has some cool gems that I was fortunate to have seen. 

Went inside a vertical cave named Jomblang near Yogyakarta and then explored the volcanoes - Bromo and Ijen. Try the blue flame tour at Ijen...one crazy experience that made me breathless, amazed, happy! 

In Bali I tried scuba diving for the first time- went to one of the BEST places on earth- Tulamben- there is a shipwreck even in the shallow part of the water. So, I saw alot...and the fishes. OMG. I was so thankful to God for making these colours on them! 

As is evident from many of my answers here, Spain is the country that's made the biggest impact on me personally through the people themselves, the culture, the food, the history, and the topography/nature as well.

If you have a car or can rent a car, this is a country to get lost in. Drive, follow your instincts, turn at random and seek places that look interesting. There are treasures everywhere - old aquaducts, Moorish castle ruins, Carthaginian cities, gorgeous hiking trails and hidden waterfalls, cliffs, beaches, gastronomic wonders, local artisians...

Driving through Spain is like Christmas, each turn opening a new surprise. Really. It may sound sappy, but every road trip there is like that.

Beautiful and unique catedral de sal located in Colombia. It is an underground church built within the tunnels of a salt mine 200 meters underground in a mountain very close to the town of Zipaquira. Really amazing place and a jewel of the modern architecture. Definitely, this Salt Cathedral is A must see place in the world!!

For me, it is a list of places you don't hear much about (or not at all) or you have to simply be there to get that feeling that gets burned into your memory forever and you will never forget it. If I have to limit it to 5 spots on Earth where I felt "eternal bliss" it would be:

1. Semuc Champey turquoise limestone pools in Guatemala (jumping down 12m tall waterfall at the end was really cool) [photos].
   
   
2. Both hiking and sea kayaking Na'Pali Coast State Park of Kaua'i [photos].
   
   
3. Central Borneo, Malaysia Gunung Mulu National Park. Visiting Deer Cave and later in the evening watching millions of bats leaving the cave was a stunning show. [photos].
   
   
4. San Agustin and Isnos archaeological parks (Easter Islands of Southern Colombia, but with smaller statues). Never heard of the place before and was very impressed.  [photos1 / photos2].
   
   
5. Two-day horse riding with my guide Holgar in the Vilcabamba mountains, Ecuador. Two guys on horses passing through quite challenging landscape, wading streams, picking wild berries, and in total isolation from the outside world. All I could ever wish for!
   
   

For many places you just have to be there. Pictures, videos, TV and blogs can get you excited, but once you get there you might feel something else or possibly don't like it at all.

China

To see the Great Wall Of China, over 5 thousand years old. Visiting and playing with Panda Bears in Chengdu, Seeing the Terra Cotta Warriors, over 2 thousands years old, and so much other ancient history is mind-boggling!!!

Hi Cellan,

I don't know what you like to do, but some highlights of my trips around the world:

Sleeping on the Great Wall Of China - this can only be done through 1 tour company who has the permits. This was absolutely beautiful; waking up to watch the sunrise and then hiking the wall... there really isn't anything like it. 

Getting to Krka right before the ticket window closed and being able to run around the park by ourselves. (park is still open 2.5 hours after ticket booth closes).

Shark diving in South Africa.

Staying in any village in Ghana and really getting to know the locals. 

Zip lining in Dominica.

Laying on the beach in Mauritius

taking a rickshaw through Old Delhi

My favorite countries have been Croatia, India, Ghana, and Dominica. 

You definitely shouldn't miss the Balkan region, it's beautiful and still very undiscovered. 

Happy travels!

- Kristal

Just saw the Great Wall Of China

Rice Terrace of Philippines Cordilleras in Ifugao province, Luzonisland, Philippines.

2,000 years old steep rice terraces which hand-made by the indigenous with great irrigation system. My picture below is really poor, true site is so wonderful!

Filipinos have called it as "Stairway to Heaven" 

Another place is Son Dong Cave in Phong Nha-Ke Bang National Park, Vietnam. The largest cave in the world.

I've been the national park but in that time, Son Dong Cave was not opened for public. See picture from National Geographic. AMAZING.

I'll start with some from my home country: 

* Clarksdale Mississippi, the home of the Delta Blues. Read up on the history and lore of this place, then pay a visit, driving out into the country to go to juke joints (or visiting some in town) is like nothing else on earth. You'll hear incredible music, eat delicious food and see a slice of Americana that isn't exactly cheerful, but is completely fascinating. 

* Stanley Idaho doesn't get as much press as some other Western mountain locations, but it is absolutely stunning. Go rafting or fishing on the Salmon River, hike to your heart's content, and go swimming at Redfish Lake Lodge.

* Duluth (Minnesota) and points north along Minnesota's North Shore of Lake Superior. This is my home turf, so I have to hype it, but there's nothing disingenuous about my enthusiasm. The forests are pristine, the lake is monumental and the drive along the shore takes you through quaint little towns. Starting from Duluth, it's also easy to head up to Ely (Minnesota), which is a great place to access the Boundary Waters Canoe Area Wilderness, a million square miles of unspoiled natural beauty that you can only explore by canoe. 

And a sampling from the rest of the world:

* The Canadian Rockies. I'll use Lake Louise as an example so there's a pin on the map. Gobsmacking beauty everywhere you turn. 

* Guatemala, one of my favorite countries in the world, hands down. Incredible culture and history, beautiful landscapes, amazing people. Antigua Guatemala is no secret and neither is Lago de Atitlan, but both are well worth a visit and you can always skitter off to a smaller town if you want some breathing room.

* Colombia was my last big trip and I was blown away. Cartagena and the coast seem to get the bulk of the attention, but this whole country is chockablock with fascinating sights and breathtaking scenery; you can really tailor a trip to your specific tastes. We chose to do the Amazon and the Eje Cafetero. People are incredibly friendly and helpful. 

* Ethiopia I'm going to sound like I fall in love with every place I go (not entirely untrue) but Ethiopia is fantastic. Had one of the most exciting moments of my life here, in Harar, where I fed meat scraps to a wild hyena using a stick held in my teeth. 

* The Dolomites, around Bolzano. If you can swing it, this is a place to rent a car and drive at your own pace through these stunning mountains. The Austrian-Italian cultural mishmash makes it interesting too, and the little villages are charming as can be.

* Laos. Start from Louangphabang or even Nong Khiaw and explore from there. Look into boat trips to small villages where you can do trekking and really get off the path. And please for the love of god, don't add to the tourist circus that tak bat has become in Luang Prabang; keep your distance, be respectful, take it easy with the camera. It's all but ruined along Sakkaline/Sisavangvong Rd. Nevertheless, if you can find a quiet side street, you might still get a glimpse of it without the throngs.