Here are a few suggestions for your next trip from Sopot(BG)

In 3 hours, you can reach Sofia, Plovdiv, Stara Zagora, Sliven.

In 4 hours, you can reach Burgas, Veliko Tŭrnovo.

In 5 hours, you can reach Pernik, Haskovo.

In 6 hours, you can reach Varna, Pleven, Shumen, Blagoevgrad.

In 7 hours, you can reach Ruse.

In 8 hours, you can reach Dobrich.