Hooray to bike paths, especially in Mladost :) I've been a biker in Sofia and Berlin/Potsdam, and yes, Sofia is uncomparably less friendly, but if you're dedicated you can still get around :) It will never be as popular as in Western Europe - just because of the hills, for older or less fit people it's difficult to do. But for everybody else it's the best option in the disastrous Sofia transportation grid. It's fast, reliable, healthy (when you watch out) and fun. And another major point is the weather - Sofia gets a huge amount of good weather days in a year, which is great for biking!