Pirin National Park covers 400 square kilometres of the Pirin mountains south of Bansko, and it is the best high-mountain hiking in Bulgaria. The terrain is jagged granite and marble peaks, 176 glacial lakes, deep old-growth pine and spruce forests, and alpine pastures that turn green and wildflowered from June into September.
The two classic day hikes both start from huts above Bansko. The Vihren Hut (reachable by minibus from town) is the launchpad for Vihren Peak, the second-highest summit in Bulgaria. The Banderitsa Hut sits in the glacial lake basin and is the easier walk — a couple of hours up through the woods to a chain of small, cold mountain lakes. Bring layers (snow can fall on the high peaks any month) and water.