schynige Platte-First
When I talk to other people I've hiked with in Switzerland this hike often comes up as one of their favorites. It certainly earns high accolades as it's a relatively easy hike that provides stunning views of Interlaken and Lake Brienz on one side and Lauterbrunnen, Grindelwald, and Jungfrau on the other. It takes you past a precariously perched mountain restaurant/hotel at the Faulhorn, the mountain lake Bachalpsee, and to stunning views at First including the famous cliff walk.
The hike is about six hours, although with stopping for pictures and such it will likely be longer, and is 10 miles with about 800 meters of elevation gain and loss. Luckily, any elevation gain is pretty gradual, and the steepest downhill is right before Bachalpsee, and it doesn't last for a long time. You can do the hike in either direction, but I recommend going from Schynige Platte to First because you will probably want to spend as much time at Bachalpsee and First as you can which makes it a better place to end the hike.
One of the biggest issues with the hike is that getting to and from the trail is a bit of a hit to the wallet. The train to Schynige Platte is a Jungfrau Railway Company train, which is the private tourist company which runs a lot of the area, and this won't be covered by a Swiss Travel Pass. You can get the Berner Oberland Regional Pass, which may be a good option if you're mostly traveling in this area, to (I believe) get the train and cable car for this hike for free. The train from Wilderswil to Schynige Platte is about an hour, but gives some great views, although you'll get the views at the top soon enough.
Once you're off the train there's a restaurant and bathrooms you can use before starting the hike. Walk around the hotel for some great views of Lauterbrunnen Valley and see the garden there. Once you've done that just start following signs to First. When I did the hike I did a small detour by going on the Panorama Trail for the first part which adds just s little bit of time to the hike. It provides some cool views of Lake Brienz down below so I'd recommend checking it out. At the trail head you'll also see a sign for the last cable car from First to Grindelwald so make sure you arrive before that leaves. Otherwise you'll have to get a scooter down or walk a couple more hours to Grindelwald.
After folllowing the trail for awhile you'll see the Faulhorn restaurant at roughly the start of the last third of the hike. You can go up for a drink and food, but it will add a bit of time to the hike. Otherwise just continue to Bachalpsee and from there it's about one more hour to First. At First you can enjoy a nice restaurant with great views, and I recommend doing the whole cliff walk there for great views of Grindelwald below. There's also a bunch of "fun park" activities here such as ziplines and scooters, but I haven't done those although they are incredibly popular. I've seen times where there's an hour queue for a rental scooter.
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