Buy tickets and join the fans at a game at Vasil Levski Stadium. If there's nothing on while you're in the area, you might like to check if there's a guided tour of the facilities.
This sporting facility in Sofia is popular with travelers, so leave a spot for it on your schedule. Don't think the sightseeing ends there, however. There are plenty more spots waiting for you to experience after Vasil Levski Stadium. Alexander Nevski Cathedral, Mount Vitosha, and Ivan Vazov National Theatre are nearby.