I'm wondering whether there is a nuance difference between "faire un tour de" and "faire le tour de". I saw examples for both. E.g. faire le tour du monde, faire un tour d'Europe. Are they interchangeable?
They are the same only for geographical entities, because the construction also have other interpretation and those can be different for some cases.
- Faire un tour de can also mean "have a ride on" (a vehicle, a carousel, a rollercoaster...).
- Faire le tour de has the literal meaning "make one's way in circle around".
As such faire un tour de carousel and faire le tour du carousel mean different thing: the former means riding on it, the later walking around it.
Additionally, you may note in that example a slight different in syntax, in that "faire le tour de" usually requires a definite complements, whereas faire un tour de doesn't.