In reply to duckling:
This seems like an odd ambition. If I was backpacking across the world I'd be motivated to go to the ten best crags.
Konala Boulderkeskus in Helsinki.
http://www.boulderkeskus.com/ (link available in English)
This is a bouldering wall. The person who runs it is an excellent carpenter and built the walls. They are really whacky and original shapes, including a giant sphere, a free standing boulder which you top out on and then descend a staircase in the middle of and many uniquely contoured surfaces. It is probably the third biggest dedicated bouldering space (a little smaller than climbing works in Sheffield) , but due to the friendly staff and the uniqueness of the walls could well be the best (I wouldn't really know as I've never been to the other contenders). Certainly the people set about making the best bouldering wall in existence.
Helsinki also has a pretty cool roped climbing wall. There are some pictures here
http://www.kiipeilyareena.com/gallery.php but unfortunately no information is available online in English. The competition wall is great. It's 16m high and overhangs 11m. There's also a 28m high sculpted wall. Is this one of the top 10 in the world? Probably not, but I would think that Konala boulderkeskus may well be.
Perhaps I'm overhyping Helsinki. But honestly, it offers the best indoor climbing I've ever seen. Feel free to ask anymore about it.