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'?

2 answers

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.