When and where was The Castle of Otranto published?

Horace Walpole's book, often considered the first gothic novel, was published in 1764 in London, England. Walpole was fascinated with the Middle Ages; the novel is set in the medieval era, purporting to be based on an Italian manuscript published in Naples in 1529. To make matters more complicated, the 1529 manuscript is said to be based on papers dating back to the years between 1095 and 1243, the height of the Middle Ages. Of course, the story is really the invention of Walpole and was written in the 1700s. 

The novel begins with the young Conrad being crushed to death on his wedding day by a giant helmet falling from the sky, a fantastic event typical of Romance, but Walpole weds this and other Romantic elements to what he hoped would be a realistic story. He incorporated what would become typical features of the Gothic genre, from a medieval setting to secret passageways to odd, scary sounds.