According to European Graduate School, Mary Shelley wrote "Frankenstein" in Switzerland while vacationing near Lake Geneva. It began as a short story, but her soon-to-be husband, Percy Bysshe Shelley, encouraged her to expand it into a novel.
Writer Mary Shelley and poet Percy Bysshe Shelley vacationed in Switzerland during the summer of 1816 along with a group of friends, including English poet Lord Byron. One evening, Byron suggested that everyone try writing ghost stories to entertain and frighten one another. Shelley took Byron up on his challenge, and the result was a scary short story that ultimately became the iconic novel "Frankenstein."