|Source: Altimetrias de Colombia|
I mentioned above that Letras is the biggest mountain pass I know of. The volcano of Mauna Kea in Hawaii is bigger - it offers 4,203 meters of elevation gain. But, Mauna Kea is not a mountain pass. And, nothing in Europe comes close to Letras. The biggest climbs I found in Europe were Gavia and Stelvio in the Dolomites, with almost 2,000 meters of elevation gain. The mountain passes in northern India and Chile are at higher altitudes (almost 5,000 meters) but the climbs (as measured from the nearby valleys) are only 2,000 meters or so.