Translation:Traveling is tiring.
True, but since many qualifications or further descriptions of the action can only relate to verbs and not plain old nouns, I'm assuming that you need the 하기 form in those cases. It's best to illustrate with some examples. If I'm right about this, then:
- 여행 (travel) - correct
- 여행하기 (travel/traveling) - correct
- 일본에 여행 (traveling to Japan) - incorrect (could be correct in a sentence but in that case 일본에 relates to the verb of the sentence rather than to 여행)
일본에 여행하기 (traveling to Japan) - correct
공부 (studying) - correct
- 공부하기 (studying) - correct
- 영어를 책 없이 공부 (studying English without books) - incorrect
- 영국어를 책 없이 공부하기 (studying English without books) - correct
Maybe in cases of adverbs (e.g. 없이), the verb can be broken up so that the adverb goes directly before 하기:
- 영국어 공부를 책 없이 하기
Not really sure if that's correct.
We are saying different things for the same effect. Think of 피곤하다 as running-low-on-energy. "To (make) tire" (what the trip does) has a causative quality, so literally it would be 피곤하게 하다, and "to be (made) tired" (what the traveler feels) would be something like 피곤해지게 하다 or 피곤하게 뒤다. Nobody uses grammar like this and says it that way, but if you ever need to explain it . . .