It's right. Каждый месяц я езжу в Исландию.
Past tense: когда я работал журналистом, я каждый месяц ездил в Исландию.
It's right too.- habit, ability
В детстве я ездил на велосипеде. Сейчас я езжу на автомобиле. Very similar to the repeated action.
And this one is right!- return trip
На прошлой неделе я ездил в Москву. (Went there and back)
Or "съездить" if you focus on successful accomplishing of your plans.Based on this explanation, I should use ездить for a roundtrip.
You take it too literally! It's not an algebra, it's a language. You went TO Iceland. Then you LEFT Iceland. => It's a round trip, that's enough for it. You are not in Iceland NOW.This trip, however, isn't about a roundtrip.
Even more to add: the whole trip (home - country 1 - country 2 - country 3 - ... - home) can be treated as a round trip. You "ездил" (or "съездил") to all those places.
I did not get the idea of this comment. What do you mean by "return trips are not necessarily implied by the word itself"?Another reason was the fact that I came across a few posts over here, according to which return trips are not necessarily implied by the word itself.