What are the steepest, highest, most miserable road ascents in the world? Lately, I’ve been “enjoying” pretty much every weekend a 9km, 650m vertical ascent near my home on my touring bike (the average grade is about 7.5%). The grueling ride has turned out to be a lot of fun for me, in a strange way.

I wondered what I might aspire to. Thus my question: what are the steepest, highest, most miserable road ascents in the world? I.e., what might be a fun long-term goal to work towards?
Road climbs are graded according to elevation change and overall length. The classifications start at "category 5" and go upto "category 1" and finally "Hors Category". Here's a list of "Hors" climbs from the Tour de France throughout its history. These are the hardest road climbs that are doable (at a non-embarrassing pace) by elite athletes.

Generally speaking, cat 5 and 4 climbs can be found in places with non-mountainous geography. Cat 2 through Hors climbs are hard to find in anyplace but very mountainous areas. If you do a cat 3 climb on a group ride-- it will be remembered and talked about. Going up a category usually means that both the grade and the distance is harder. I believe that hors category climbs are sometimes classified as such because of the conditions of the road (eg gravel/dirt is much harder at 15% than asphalt).

You can see informally categorized grades if you use the Strava app (it tells you the category of the climbs you did on recorded rides). If you're interested in challenging yourself this is an excellent way to measure and compare progress because top times are recorded for each categorized climb.

Here's an example of a ride with very heavy climbing yet "only" cat 3/4 hills, it was the Rapha 2011 Gentlemen's race (video). For non-elites, this would be a tremendous accomplishment.