Kapfenstein is a municipality in the district of Südoststeiermark, in the Austrian state of Styria. It lies in the southeastern part of Styria, a region known for its rolling hills, vineyards and volcanic landscape near the border with Burgenland.
The municipality is best known for Kapfenstein Castle, a hilltop fortress that gives the area its name and is a local landmark. The surrounding countryside is part of the Styrian volcanic region, an area shaped by ancient volcanic activity and now characterised by agriculture and wine production.