According to Maria Lemos, the founder of the Athens boutique Mouki Mou, it’s all about “philoxenia,” a love of one’s guest.

The author and illustrator Oliver Jeffers invited friends to toast his new book at a dinner in a former textile mill.

Adam Shapiro and Gautam Rajani, the founders of the clothing brand SMR Days, invited friends and family back to the Spanish island where they got...