It's literally a door-to-door... even tougher than Mortirolo itself. I discovered it thanks to the Granfondo Santini Stelvio. The climb's stats speak for themselves: 11.73 km with an average gradient of 10.5% and a vertical drop of 1,231 meters, with ramps reaching 20%.
It starts in Sernio, a town in the Valtellina valley right next to Tirano. It passes through the small village of Boilo, a very narrow, cobbled pass... and from here the spectacle begins. The road is narrow, even narrower than the Mortirolo road, and is in perfect condition.
The toughest sections of the climb are the beginning and end, where impossible ramps appear. The last 2 km are very, very tough.
From Passo Guspessa, it connects with the road that connects Monte Padrio with Mortirolo.