With its Thracian and Byzantine history there are enough sights of interest. Overall, I liked the South the best.
Visit #3
2021 (June): A few days in and around Plovdiv by rental car (Pirin NP, Kazanlak, Bachkovo).
Visit #2
2018 (September): Four days near the Black Sea coast with the WH community.
Visit #1
2004 (July): A weekend in and around Sofia.
World Heritage Traveller 