Due to orientation of site (WNW) reasonable flying starts not before 1600.
If there are no (commercial) tandempilots on the train, most probably conditions are unsuitable...
Access
Take late afternoon train from 'Wilderswil' and get off at 'Breitlauenen'; just follow the (commercial) tandem pilots ;-)
Timetable: https://www.sbb.ch
Rules
Due to the helicopterbase at the airport, special flight rules are in place; details here (for overview see pix):
http://www.deltaclub-interlaken.ch/Fluggebiet/
Airspaces in Switzerland are a tough subject, get all the info you can get before flying: http://www.flyland.ch.
DABS (active danger areas etc): http://www.skyguide.ch/de/nc/services/aim-services/dabs/
Download of area info (as PDF):
https://www.shv-fsvl.ch/en/fluggebiete-sicherheit/fluggebiete/fluggebiete/
> Bern > Interlaken
WEATHER
Föhhn!!
Weather info:
- act wx 'Niederhorn': http://m.windline.ch/meteodata.php?stationID=4109
- act wx 'Grindelwald-First?: http://m.windline.ch/meteodata.php?stationID=4104
- Wind etc: http://www.meteoschweiz.admin.ch/home/wetter/messwerte/messwerte-an-stationen.html
>> zoom in for winds on Jungfrau etc
- Föhhndiagramm: http://www.meteocentrale.ch/de/wetter/foehn-und-bise/foehn.html