I think the biggest thing is the exposure to different things as you travel. As someone else mentioned you are exposed to different cultures and customs, eve if you are just traveling in your own country. We learn so much by doing and observing, what better way is there than traveling.
The actual travelling also provides opportunities for kids to learn how to read maps, estimate mileage, calculate gas mileage, and read road signs. People can research destinations and read to decide what activities they would like to do in the new place.
When you travel to a new place you have a chance to learn how to navigate around the new location. There are probably points of interest that can be visited, such as museums or libraries. There is always a lot of learn in those types of places. Even amusement parks such as Sea World, or aquaria and zoos, have lots of educational features.
Just the mere fact of being away from your "normal" place and routine makes you learn how to adapt to the new place and routine.
More than ever before, traveling is a form of learning. With the globalization of information and more efficient travel, it's more likely than ever before that a person will have some personal (or virtual) exposure to people from other countries. Traveling to other places is an opportunity to experience the culture, the language, and even the politics and government of people who are probably unfamiliar. Just that basic understanding, that it's not simply a language which separates people from other cultures--that other places and other people are not necessarily like the people and cultures you know--is a significant advantage to being able to adapt to a globalized world.
On the other hand, traveling also allows people to discover the inherent similarities among people of different cultures. Look at it from this perspective: despite the differences in language, the diversity of cultures, and the disparity of politics and governments, people are essentially the same. Human nature is human nature. Traveling is, indeed, a learning opportunity.
Travel is a form of learning because it exposes (or can expose) a person to cultures other than one's own and to places that have historical or cultural significance.
If a person travels to foreign countries, he or she may (if they pay attention) come to understand more about how people from other countries live. The traveller may come to understand what sorts of material lives the people have and what sorts of attitudes they have towards various things.
If a person travels to historically relevant places, he or she can learn more about the past. For example, I have travelled to the sites of ancient Native American pueblos, which taught me things about their lives. I have also been to scientifically relevant places that allow me to learn about geology.
Traveling is a great method of learning! Traveling around the world lets you experience things that you haven't seen or heard of before. Meaning you'll learn something new, every step you take! I also learn that if you are learning a language, it is good for you to talk to other people in that language, because you'll learn a lot from it. Since you'll be at their country then you'll must talk to them in their language. Also this is a little risky but, going to a country without speaking their language at all. You'll learn the responsibility and you'll probably learn some safety rules in the future if you get lost. When you travel you'll learn about their culture which is very special. Learning about someone's culture will let you get to know them better, and how they respond, to things. On the way you'll learn about their religion too! Religion is a big fact in everyone's society. The religion that they believe will set rules for them making the outcome of the person different. In my personal experience traveling around the world, Taiwan, Korea, Japan, and etc. Let me to believe that every culture and religion in different places of the world can be similar yet different. They add or take away some part of religion that makes it fascinating. Their culture are similar but very different. I recommend going around the world going to different countries to experience what it is like to live there. Going around countries also entertaining while you learn about the different things that goes around in their daily life. Since I grew up in America, my parents grew up in Taiwan. Whenever I needed help in Math, they also try to help me. Of course they teach math in Taiwan way different! Different formulas, which sometimes does help me. Thus meaning every country on Earth is very different and should be explored not just through pictures, but by going there yourself! The food in different areas is different and it's good to learn about the different food that they eat.
You can learn about their religion, culture, society, math, and the different food that they eat.
Hope this answers your question!
Traveling is undoubtedly a very rewarding learning experience. Just as what an ancient chinese saying said - "traveling ten thousand miles is equivelant to reading ten thousand books". I guess this type of learning is probably more engaging and entertaining compared to conventional class room way of learning. It is not only about what you observed but also about what you felt about. In order to turn knowledge into long term memory, the most effective way is to adopt as many ways of learning as possible including sensory (visual, auditory etc), kinesthetic and even emotional approaches. Presumably, travelling allows individuals to learn best through exploiting these versatile types of learning along with unique and enjoyable travel experience.