St. Petersburg - Helsinki - Stockholm - Oslo - London - Paris - Bordeaux - Marseille - Barcelona - Rome - Milan - Zürich - Cologne - Amsterdam - Hamburg - Berlin - Munich - Vienna - Sofia - Athens - Budapest - Prague - Warzaw - Gdansk - and home again.
But: I sincerely recommend that you even pass Copenhagen, when going from Oslo to London. You wouldn't want to miss the Little Mermaid, even if you aren ot interested in fairytales. I live in Sweden, so I know that there are good connections.
Furthermore - when in Barcelona, you MUST NOT forget to visit Gaudis church, La Sagrada Familia, which maybe is the best sight on all of your journey. You'll see the light there, litterally, without even being religious.
Talking about churches - an even more important landmark in Vienna is St. Stephans, in the very center of the city. It is my home town, so I would advise that you spend a week there. PM me, so I can give you some hints of what to do. Or you can taka a look at my web empire, where I write about Vienna: VIENNA
Finally, going from Vienna to Sofia, why not pass lovely Ljubljana in Slovenia and then make a stop in Belgrade, as it is directly on your route. The Triple Bridge in Ljubljana and the Dome of St. Sava in Belgrade surely are worth a visit. And why not spend an afternoon at the castle in Belgrade, where the power of the Ottomans' was broken in the early 18th century?
However, I wish you a very nice trip, I would love to do this myself!!!
COM05 - Cylinder Head