1. I'm going to travel to Europe this summer vacation.
2. I'm going to travel in Europe this summer vacation.
Which one is corect? Do I have to use 'in' or 'to'?
Both are correct.
The first sentence emphasizes the journey with the use of "to." The second sentence emphasizes the travel within Europe with the use of "in."
Both are grammatically correct. However the first one means that you are outside Europe and are going to go there. The second one means that you are going to travel inside Europe.
Both sentences can be correct depending on the intended meaning.
1. "I'm going to travel to Europe this summer vacation." This sentence suggests that you are traveling from a place outside of Europe and your destination is Europe. In this case, you are indicating that you will be going from one place to another.
2. "I'm going to travel in Europe this summer vacation." This sentence suggests that you are already located within Europe and you will be traveling within different cities or countries within Europe during your summer vacation. In this case, you are indicating that your travel will be within the boundaries of Europe.
So, the choice of using "to" or "in" depends on whether you are traveling from outside of Europe to inside Europe (to) or if you will be traveling within Europe itself (in).