One of the many starting points for an excursion to Sveta Trojica ("Mount Trinity") is in Postojna itself, although the two most popular routes are those that begin in the villages of Petelinje and Trnje pri Pivki.
Various footpaths lead to the summit, from where a wonderful view opens up across the whole of the Pivka Basin and the nearby peaks of Snežnik, Nanos, Vremščica and Planinska Gora. On a clear day you can see all the way to the Adriatic.
The climb up to Sveta Trojica is an easy one and the well-marked path runs through shady pine and beech forest.
At the summit stands the pilgrimage church of the Holy Trinity, mentioned by Valvasor in the 17th century.
From Postojna the hike takes approximately 3 hours and 30 minutes, depending on how fast you walk.