From Valtopina climb to Serra Castle, then passing through Vallemare you will reach the town of Armenzano. The trail continues from the drinking trough upstream Armenzano: it climbs quickly, to the extent that it is considered a very direct trail.
Once you reach a large deep valley, follow it upstream keeping the left, passing near the doline of Mortaro delle Trosce.
Texts and photos taken from "Parco del Monte Subasio", Quattroemme, Perugia 2006. All rights reserved.