Access
Train from Interlaken: https://www.jungfrau.ch/en-gb/jungfraujoch-top-of-europe/
>> pretty expensive; very early morning departures sometimes cheaper...
Rules
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): www.skybriefing.com/portal/
Many special regulations in force in this area to keep base jumpers, helicopters, paragliders etc separtated! (ie when landing in Interlaken)