https://www.strava.com/segments/13842987 A road called Adamastor, 5.6miles, 8% avg gradient, 2266ft of climbing. Without a doubt the hardest. I rode this as part of granfondo living at sea level made this one super hard for me, my HR and RPE were at threshold when my watts were only around 200 (I had an FTP of 275-280 at the time). My HR averaged 165bpm for just under an hour, and it's generally there when I'm riding threshold. The low cadence up the climb then caused my legs to cramp following a long descent, so that kind of put a damper on the rest of the fondo. Would love to do it again, because it was awesome, but would want to get a hold of an altitude tent to try and acclimate beforehand
https://www.strava.com/segments/7819548 this climb was a cat 2 climb (at which I could be at the summit an hour after leaving my parents' home) and much more pleasant, and only near the top did I start to notice my HR spiking from the altitude lol