In every game in the series, you are trying to create a sequence of contiguous countries/states/provinces while different vehicles like planes or cars can help make connections. There have been seven games in the series, although some of them weren't in English. I think. And, actually, it doesn't matter since place names are the only words in the games :D
About twelve years ago, I wrote a review of 10 Days in Africa: https://boardgamegeek.com/thread/89054/light-enjoyable-game-geography Rereading it, I'll still stand by that review.
The 10 Days series is not Alan Moon's best game design. (Or Aaron Weisbaum's, for that matter) BUT I do think it's one of their more important designs.
Rule wise, the 10 Days series is very, very simple. They are games that you can teach to just about anyone, children and teens and adults. They are accessible enough that non-gamers can be competitive while tense enough that seasoned gamers can enjoy them.
If that's all the 10 Days series had to offer, that'd still be pretty good. However, in addition to teaching cognitive reasoning skills (which hopefully most games will teach), the 10 Days series also legitimately teaches geography. Pulling that off while being fun is a pretty impressive feat.
While Edutainment has come a long ways in the last few decades (What can I say? Bubble Guppies impressed me when our son went through a Bubble Guppies phase) but a game that really works as a game that is very educational is still no mean thing. The 10 Days series can work as a standby in most game libraries and classrooms.
At the moment, it looks like the US map is the only one available in the US. Which is a shame and I hope that changes. I am glad, though, the series is still out there.