Get in touch with the guys who run 360 Valtellina bike and arrange an uplift day. Not only will they be stoked to share Basso Valtellina's sickest and most gnarly descents, they're also a great laugh.
Here'a an jaw-shaking, adrenaline-inducing major descent off the Passo San Marco. Best to have a guide if you're not sure about the terrain. Steep and slippery.