Only free people can be happy.
In this movie, there is a foreign naturist couple heading home from a French naturist resort (don't know wich one). She is sleeping in the RV while he is driving. When a tire gets flat and he stops to replace it, she goes out sleepwalking, without beeng seen by her husband. When she wakes up, she finds herself in a country side, naked and knowing no word in French... She is discovered by a boy (the famous Lulu from the title) who helps her to find her way.
Unfortunately, it is not a story of a lost naturist, but a story of the boy, where the meeting with a naturist is just a 'trigger' of his adventures.