Passo Castrin
Rather long and tiring itinerary, but also a lot of fun. If done in autumn it gives the magnificent warm colors of foliage. The first part is a long asphalt climb to Palade pass (but with variations you can climb almost all of it off-road).
From the pass, then descend on trail to Senale and climb to the Castrin pass, first on trail with a short push section (bypassable on forest road by extending a few minutes) and then on forest road with a few very steep, cemented climbs. At the pass climb up to the Castrin hut (inquire about opening times) and then descend on forest road and challenging trail to the first farmstead. Here there is an interrupted trail sign, but you can continue, the trail is very nice, all with wide switchbacks in the forest and paved sections. At San Pancrazio go up briefly and take a nice false-floor path, then descend on asphalt and path to Cermes. From here on bike path to Merano.
Itinerary for experienced and well trained bikers, if done with ebike it is perfect to pass the very steep sections.