The legendary Mortirolo Pass, which despite "only" standing at 1852 m, presents stretches with gradients of up to 23%! The climb, also made famous thanks to the great Marco Panatani, can be tackled as follows:
from Mazzo di Valtellina, with a 12 km climb and an elevation difference of 1300 m;
from Grosio (Tiolo district), with a 14 km climb and an elevation difference of 1100 m;
from Tovo Sant'Agata with a 12.5 km climb and an elevation difference of 1300 m (and a maximum gradient of 23%)