I have been to more than 100 countries by the age of 30. That is an achievement that I can only dream of when I was young. But I would not stop! There are so many places you could go and there are so many sceneries that worth chasing for. Some people travel for history, others travel for religious reasons, and some people travel for the sake of travel...me, I think I travel largely for geography.
Geography is an interesting topic. With the understanding of geography, you could gain knowledge of history, biology and humanity. The possibility is endless.
You may ask, what if you are tired one day? No way. Maybe by that time, I will do what others have been doing: travel for the sake of travelling!