Typically, this would have been the day of the cirque de la solitude. Superb hike and one of the mythical stages of the GR20. Unfortunately, this section of the trail has been permanently closed. We were disappointed not to be able to do the cirque again, at least until we had done 10 minutes on the Mont Cintu trail.
Our book didn't describe this section of the trail; we learned from a sign at the start that it's an 8 to 10 hours day (8 hours normal, 10 if you decide to climb the additional 150m to go to the summit) that goes through Mont Cintu (the highest mountain in Corsica). We chose the standard because when we reached 2456m, we said that was high enough. Note, we didn't climb 2500m that day, that's a bit intense. We climb to Bocca Crucetta (2456m) from Asco (1500m), then descend to Tighettu (1700m). So it was a day of +1000m and -800m. Everything is very steep and technical. Think of climbing a problematic mountain twice: once on rock and on scree the second time. After that, you have the equivalent of half of Mont Ste-Anne to do on rock, scrambling. It's the same for the descent, minus the rock part.
This is where everyone should be thinking, "Sounds really boring and difficult as a hike.” You're half right: it's difficult but so, so not boring. The part we tend to forget is that in Corsica, above 1000m, there's little vegetation, so you have a splendid view the entire time on your hike. Mont Cintu offers breathtaking views! My conclusion after the experience sums up like this: "Forget about the cirque de la solitude, Mont Cintu is so much the best route!"