From Sondrio you'll first ride the Passo Aprica before a long, swooping descent to Edolo. From here it ramps up gentle to Monno before a steep climb under a canopy of trees takes you up towards the Passo Mortirolo. You'll ride a few kilometres along the top before hitting the pass sign and the top of the much steeper side. Start going down that descent but take a right turn towards Grosio. Safer and a lot less steep, this narrow downhill pops you out on the far side of Grosio. From here, follow the small roads or even the Sentiero bike path back towards Tirano and Sondrio.
The Mortirolo doesn't usually open until late May/early June.