If you want to escape the pace of the city you can go to Mount Vitosha, whose peak is visible from multiple spots in the city. Here you can enjoy a hike through the forested slopes or rocky peaks, and even go rock climbing if active pursuits are a thing for you.
In Vitosha mountain one could find easy and not that easy trails in any season of the year. If you love hiking, biking or just having a short walk in the nature, this is a must visit place while you are in Sofia.
It`s easy accessible, only 1/2 hour from the city center you could be on the top of the mountain.