Evening is the right hour for the Sihlsee. When the sun drops toward the Zürich side, the light slides along the reservoir and picks out the farmhouses on the far shore, and the hills turn a layered blue. A sunset run from Hirzel or Einsiedeln would end naturally here, with a quiet stop by the water and a long look at a view that fades from gold to grey.
The lake is man-made, finished in the 1930s to store water for the railways, but it has the soft ease of a natural one. To the south the twin peaks of the Mythen rise above Schwyz, and to the north the hill of the Etzel stands over the shore, with an old pilgrim chapel on its flank. The Etzel is part of the Way of St James, and walkers heading for Einsiedeln pass this way carrying shells on their packs. In the evening you may see herons standing at the water's edge and swallows skimming the surface for insects.
Swimming is possible in warm months, and in summer the shore has a few spots where you can wade in from grass or pebbles. After sunset the water holds its warmth for a while, and the surface can be glassy, with reflections of the sky. Fishermen sit patiently at the edge, and the occasional paddleboarder glides by. In late autumn the lake can be steely and cold, with mist rising from the surface at dawn.
The roads around the lake are good riding, with gentle bends and a smooth surface, and at dusk the traffic is light. Keep an eye out for deer, which sometimes cross near the wood edges, and for cyclists without lights on the lakeside track. Shortly after the sun goes down the temperature drops, so a spare layer is worth carrying.
Einsiedeln, about three kilometres away, has the nearest fuel and a good choice of restaurants and bakeries. Feusisberg and Schindellegi on the north side have further services. If you are planning a late meal, check ahead, because Swiss kitchens close early outside the larger towns.
When the last colour leaves the sky, the lake becomes a dark mirror and the lights of villages appear along the shore. That is the moment to pull on your gloves and head home.