Sofia

For something different you could try Eastern Europe - Fly to Sofia, take the train to Veliko Tarnovo, my favourite city.

Sofia was great too. I really liked Rila Monastery and the National Park.

However, I absolutely loved Sofia and easily filled 4 great days there. We did do a day trip to Rila Monastery too, which was absolutely stunning. To answer your question, don't leave Sofia straight away. At least split your time. Because it's great. Lovely people, superb food. Plenty to explore.

If you're there for a week I'd go to Sofia, do the Boyana Church and the National Museum of History on one day as they are close to each other up the hill, maybe book a day tour to Rila Monastery and/or Rila National Park, maybe another day of stuff in Sofia, then take the train to Plovdiv which was an ancient greek city and see the sights there.

If you want to do a fast-paced Balkan loop, I’d consider choosing cities in a route something like Bucharest-Brasov-Sighisoara-Sibiu-Timisoara-Belgrade/Novi Sad-Pristina-Skopje-Sofia-Plovdiv-Veliko Tarnovo-Bucharest