The Tour d'Aï (2,331 m) is the most striking summit on the ridge north of Leysin, a sheer limestone tower visible from across the Rhône valley. The walk up from La Berneuse via the Lac d'Aï is one of the best half-day mountain hikes in the area — about three hours each way, with one short scrambling section near the top.
The final pitch is graded for sure-footed walkers with a head for heights; if you don't fancy the scramble, the lower path along the cirque past the Lac de Mayen is almost as scenic. From the summit the panorama takes in the Mont Blanc massif, Les Diablerets, and the deep U of the Rhône.