Melting glaciers are a major threat as huge chunks of rock have crashed down into the valleys. Once it was the glaciers themselves that were feared. Centuries ago, Swiss mountain dwellers prayed they would disappear. Now they pray for the opposite and the Pope has given his blessing.
You could opt for dinner in Grindelwald before taking a late train to Interlaken. Options include Onkel Toms Huette, renowned for pizzas, particularly good after all the fresh air.
Alternatively, take an earlier train back down to Interlaken in time for dinner there. The Steinbock steakhouse by the river gets rave reviews.
8:30 a.m. - After a hearty breakfast of Bircher muesli, head for Jungfraujoch.
From Interlaken Ost, a train just after 9 a.m. will get you to the top for around 11:30.
There are two routes to choose from - via Grindelwald or via Lauterbrunnen and Wengen. Ascending via Grindelwald leaves you the option of travelling down via Lauterbrunnen for a change of idyllic scenery.
For much of the route, you're on a cog wheel railway, which after a change of train at Kleine Scheidegg, hauls you through a series of tunnels. A viewing platform allows you to look out on the North Face. Expert climbers can get out and climb it.
The section from Kleine Scheidegg lasts around 50 minutes and is complete with tourist commentary.
In-your-face tourist content continues on arrival, when activities on offer include touring an ice palace, ski lessons, dog-sled rides, and an observation post named the Sphinx terrace, with stunning views.
The viewing terrace is part of a high altitude research centre (not open to the public), which anxiously monitors the retreating glaciers.
If the weather is changeable and you're exhausted by the altitude, you could dine at one of the restaurants near the railway station. The more adventurous option is to follow the signposts for a roughly one and a half hour walk through the snow to the Moenchsjoch hut.
At an altitude of 3,658 meters, it is one of the highest huts owned by the Swiss Alpine Club and you'll almost certainly see climbers arriving to stay the night or leaving for an expedition.
You can content yourself with just watching from the restaurant with yet more breath-taking views.
Around 4 p.m. - Time to descend. If you take the Lauterbrunnen route down, you could stop for a wander and dinner in Wengen, one of Switzerland's few car-free villages, famous in winter for high-speed down-hill skiing.
Many of the restaurants are in hotels and many offer traditional Swiss roesti, guaranteed to fill you up.
Trains run until around 10 p.m. to whisk you back to Interlaken before an early train or plane back home.