Nature reserve Trojmezná Hora ("Three Landmarks Mountain") consists of Trojmezná mountain ("Mount of Three Landmarks"), Plechý mountain and Plešné Jezero (Plešné Lake). Its area is 400 ha.
There are many protected forests and geological formations including the morainic Plešné Jezero lake. In several places there are growths of mountain pine and several rare species of animals and plants can be found here, which are protected as well. The technical site of this region is the Schwarzenberský Kanál (Schwarzenbergs' Canal), which leads not far from Plešné Jezero lake.
The reserve is in the Zone I of the National Park Šumava (Bohemian Forest).
The red marked sierra trail leads from the small village Nové Údolí through the peak of Plechý mountain to this area.