This is a beautiful cathedral in the heart of Sofia, a popular tourist visit, there are catacombs that can be seen with booking of a tour.
The main touristy street in Sofia and basically all of the little streets around it. Stop by for some coffee, gelato, or various delicious foods.
One of the most beautiful monasteries in Bulgaria. It's located in the Rila Mountain where people go and hike the 7 Rila Lakes as well. This is located about an hour and a half outside of Sofia. Perfect for a day trip with car or tour. The link is to a guided tour from Sofia for around $26.
Guided day tour to Plovdiv, Europe's city of Culture in 2019 for $33
If you're feeling extra adventurous, there is a day tour to Skopje from Sofia. It's 12 hours long and $164 per person.