One of the local sportives around here runs up a climb called Burrington Combe. Go a look it up on strava or OS maps, it's a miserable thing that just goes up and up onto the Mendip Hills. You get to a point where you think you have beaten it, do one more kick around the corner and discover you are barely half way up and the second half is the steepest part.
Tough guys and pros (like JTL, Dan LLoyd and others) use this climb to train on, as it is so horrible, and yet the sportive organisers take a bunch of leisure cyclists up the damn thing. Why?
Yeah the top of the combe is actually only half way. It's 2.5 miles from top to bottom. I've cleaned it on my fixie