This route is an excellent half days walk above Leysin. It can also be combined with an ascent of Tour d'Aï for a longer day. By doing Tour de Mayen on its own the height gain for the day is just under 700m.
From the 'Grand Hotel' station in Leysin, walk down past the American College and the Hiking Sheep. Opposite the Grand Chalet there is the beginning of a path.
The beginning of the route from Leysin is the same as to climb Tour d'Aï, but I will repeat it here.
Follow this path and when it splits, take the left hand fork climbing above the cliffs. The trail is well used and will climb through the forest before reaching a trackway.
Once you have joined the trackway head left until it joins a road (about ten minutes walking). Once you have joined the road turn right (turning back on the direction you have come). The road passes through a farm and pastures and eventually leads to Téte D'Aï, the top of a chairlift and summer village. Before this however there is a path, which follows a ski run up below La Berneuse to lac D'Aï and is a faster option.
From Téte D'Aï follow the trackway, which heads east and around the first cliffs which lead up to Tour D'Aï, following signs for Lac de Mayen (and not the trackway heading back down to Leysin). This beautiful lake will come into view at the same time as another series of buildings, which includes a cowshed.
From these buildings pass through the gate into the field leading to the edge of the lake. The path to Tour de Mayen heads parallel to the outer fence. If you lose the path take a bearing and sure you remain in between the fence on the right and the sole building higher on the hill (to the right and below the first cliffs on the Tour). The path will become visible shortly after this.
The route traverses east below the Tour and after the peaks of Truex and Tour de Famelon come into view a second path will split off heading up and west. Take this and it will lead around a basin and underneath a series of cliffs. After a time it will come to the lake between Tour de Mayen and Truex.
From the lake take the path heading up west. This will cross a snowfield and lead onto a ridge. After this the path crosses over to the west side of the Tour and heads down below the western cliff face. You are also now above a cliff face that stretched to the head of the valley between the two Tours.
Continue to follow the path and after a small section of chain work and scrambling it will wind up to the wide and flat summit.
Water and good boots. In winter time the route will be a lot more demanding.