The Plateau des Glières holds a special place in French local – and national – history. A limestone plateau on the Bornes Massif, the Glières was an important site of the French Resistance during the Second World War. The plateau’s location – and inaccessibility – made it an ideal location for arms supply drops by the British. After three drops in early 1944, the Battle of Glières left 121 dead as the resistance faced 5,000 German & Vichy soldiers. The site now boasts a memorial built in 1973.*
Personally, I was originally drawn by the promise of a 10 km climb averaging 10%. I was pleasantly surprised when the ride out past Thorens-Glières was beautiful. Heading out from Annecy, take the D5 towards Thorens-Glières as the road winds through Annecy-le-Vieux and around the base of the imposing Parmelan. The route is generally rolling as you approach the base of the climb, the cliffs rising on both sides as you head deeper into the valley. If you are lucky, you might catch a waterfall cascading over the edge.
The climb itself is mostly as advertised: a slow grind, averaging 10%. Luckily, if it’s warm, you’ll be in the shade, which while you miss the views, tends to make the climb itself more comfortable. And even more thankfully, it ends at around 7 km, rather than the 10km a lot of people will tell you. 
Realising you’ve reached the edge of the plateau, the sense of relief is palpable but don’t stop and hang around, cruise down to the plateau itself for a fairly gentle false flat till you reach the Resistance Monument. Like so many climbs in the Alps, the Plateau hosts nordic skiing in the winter. And when we were there, it was hosting hoards of school kids visiting the famous local site. If you are keen for a longer loop, I believe you can descend the other side of the Plateau but most of the time, people treat it as an out-and-back ride from Annecy.
On the return, you’ll do well to remember that despite being an out-and-back climb, there are still some short rolling sections on the way home. My tired legs felt every one of them!
https://www.strava.com/activities/579968570
*All of this information has been gleaned from Wikipedia. Absolutely none of it has been verified independently so feel free to correct me https://en.wikipedia.org/wiki/Gli%C3%A8res_Plateau
Frouleur 