Hi Silver!
The preposition "to" indicates that you're traveling /to/ the destination. The preposition /in/ is generally used as a preposition when discussing you're transportation. If you want to talk about traveling around a country or destination once you're there, you'd likely use "within" or "around" to express that.
For example:
I'm in the United States right now, but next week I'm traveling *to* Germany.
Once I'm there, I'll travel /in/ a car.
Because I've rented a car, I'll be about to travel /around/ Germany easily. There's a lot to see when traveling /within/ Germany!