Sofia has numerous temples. You can visit a service or visit them as cultural monuments. The oldest ones - “Sveta Petka Samardzhiyska” and “Sveti velikomachenik Georgi” are built during Roman times and the pre-renaissance murals of the Boyana church are indeed unique. 
The cathedral “Sveta Nedelya” is the impressive seat of the Sofia diocese. 

In the center of the capital you can find in close proximity temples of the four biggest religions in the world. Orthodox and catholic churches peacefully cohabitate with a mosque and a synagogue in the heart of the city.

It is also worth to visit the Russian church and the “Alexander Nevsky” cathedral.