Society Central

I have a client looking at something we're not even sure is a thing. They are a family of 5 (4 adults and 17-year-old) wanting to sail from Barcelona north along the coast for 4 nights on a private boat for just them. Not sure how far they could get - maybe all the way to Monaco/Nice in that time?? The vision is sailing at night and spending days in ports - like a cruise would be but a small boat without other people. Money is "no object" (within reason, that is). Anyone have any idea where to start or if this is a unicorn or perhaps not even reasonable?