Bulgaria's two main cities are dramatically different. Best done as a 5-7 day combined trip.
Sofia — capital and base
Sofia is the modern capital — Alexander Nevsky Cathedral, Vitosha Boulevard shopping, Vitosha Mountain 30 min away. Stay in Centre. Best for: 2-3 nights, sights focus, mountain day-trips.
Plovdiv — UNESCO and Roman
Plovdiv is one of Europe's oldest continuously-inhabited cities — Roman amphitheater (still in use), UNESCO Old Town with Bulgarian Revival houses. Stay in Stariya Grad for the photo or Kapana for food. Best for: 2-3 nights, photo-and-food focus.
Combined 5-7 day trip
- Day 1-3: Sofia (city + Vitosha Mountain or Boyana Church day-trip)
- Day 4-6: Plovdiv (Old Town + Bachkovo Monastery day-trip)
- Day 7: Buffer / Rila Monastery day-trip from Sofia or Plovdiv
Transport
Sofia ↔ Plovdiv: 2h 30min by train (cheap), 1h 50min by bus. Both run frequently.
Cost reality
Bulgaria is among Europe's cheapest. €40-€90/night for decent hotels. €10-€20 dinners. The whole trip costs less than 3 nights in Paris.
Best season
April-October. Avoid August (Sofia daytime highs over 35°C). October has warm days and cool nights — best month overall.
What to skip on a 5-7 day trip
- Bansko / Borovets ski resorts: Different trip; only worth it for ski.
- Black Sea coast (Varna, Burgas): Different trip; combines poorly with the city focus.
- Veliko Tarnovo: Beautiful but adds another 2-3 nights minimum. Save for 10+ day trips.
For Eastern Europe context see Eastern Europe by country.