From
https://www.cyclinginflanders.cc/flandrien-challenge#!
“Flanders, the heartland of cycling, is calling you for an unbelievable experience. Hit 59 iconic berg & cobble segments, marked on the road and tracked online, in less than 72 hours.
If you succeed, we’ll make you a legend: with your own personalised stone on the wall of fame of the Centre Ronde van Vlaanderen in Oudenaarde.”
This looks quite tempting for an ego-boost. I’ve ridden the Ronde van Vlaanderen sportif and really enjoyed the pave and bergs. I suppose this is the next step up with about 5500m altitude gain in a bit over 400km. Being a permanent, you don’t have to weave your way around the middle-aged blokes also having problems up the steep bits during the Ronde and might even have decent weather.