Hi
I fly once a month to Germany to spend time in FKK
If you are in London, best deal I have found (price and timeline) is germanwing from heathrow to dusseldorf. flight on saturday at noon return sunday at 3pm ish
with this flight, you are in a club around 4 pm on saturday, you can leave the club at 1 or 2 am on sunday, have a resting sleep before going back to London.
From Dusseldorf airport, rent a car and you have plenty of clubs around 30 to 60 min drive