which train station out of lauterburnnen

If you are staying at Camping Jungfrau in Lauterbrunnen, you can walk a mile or 1.2 kilometers to the Lauterbrunnen train station.

There is only one train station in Lauterbrunnen with multiple platforms for trains going in different directions.

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Use the SBB website it will show you what platform your train to Interlaken will be on.

Also there is a board with all the departures at the Lauterbrunnen train stations.

There is only one train station in Lauterbrunnen. If you are searching on SBB, it also shows you bus stops, cable car stations, etc because it shows all transport in Switzerland, not just trains.. If you select starting point as Camping Jungfrau, it will therefore show you the bus to the train station (bus stop Lauterbrunnen, Bahnhof) as the first leg of your journey. If you are going to walk from the campground instead, just enter your starting point as plain old Lauterbrunnen.

Google map is your friend

In Switzerland the principal railway station in a town is just named after it. The SBB site however know all public transit stops, so you see a lot of stops like "Lauterbrunnen, Camping Jungfrau". General rule: If it has a comma in it, it is a local bus or tram stop. These are always named "town name, stop name". On the bus stop only the stop name, not the town name is shown.
So "Lautebrunnen, bahnhof" is not the railway station, but the bus stop in front of the railway station. On the bus stop itself it will just show "Bahnhof".

If you are not sure what the best stop is to start your trip just enter the street address, or the Point of Interest in the trip planner. You can usually just enter your hotel name for example.

And if you are staying at Camping Jungfrau, you would be best served by just walking to the station rather than waiting on the bus. It is not very far at all. When we stay in town we often go to the restaurant there for dinner. An easy walk.

Its a smaller town thank you might think.