Bachalpsee is a shallow pan of snowmelt at 2,265 metres above Grindelwald, in the Bernese Oberland, and on a windless morning it holds a wall of rock and ice upside down. Almost everyone who photographs it gets the mountains wrong. Grindelwald's poster trio — the Eiger, the Mönch and the Jungfrau — stands behind you here, out of the picture altogether. What lands in the water is a different wall: the Wetterhorn, the Schreckhorn's sharp pyramid and the Finsteraarhorn behind them, with the Grindelwald glacier spilling down between. The Schreckhorn is the northernmost four-thousander in Europe and the Finsteraarhorn the highest peak in the Bernese Alps, and neither is the one on the postcards. The walk out is easy enough to do in trainers. A stony path leaves the top of the First cable car and takes you three kilometres across bare rolling pasture — no trees, just turf, rock and the whistle of marmots.
The window is hours rather than months. Still air is what it needs, which in practice means the stretch after sunrise, and a breeze pulls the peaks apart within minutes. For a few weeks from late June you walk through alpine roses, a low rhododendron with rust-backed leaves that flowers deep pink, with gentians in the shorter grass between them. By October the ground has gone brown and the wall has taken its first fresh snow. Beyond the water the path climbs another hour and a half and puts you at the Faulhorn, where a stone inn has been taking guests since 1830. Nothing reaches it by road, so everything still arrives on foot, by mule or by helicopter. The other thing the photographs never show is that this is not one lake. A low rock bar crosses it, and most people stop at the near shore, take their picture and turn back. Over the bar, a second basin opens six metres lower, with its own shoreline and a single stone hut.