The Castle of Otranto by Horace Walpole

According to Wikipedia: "Horatio Walpole, 4th Earl of Orford (24 September 1717 – 2 March 1797), was an English art historian, man of letters, antiquarian and politician. He is now largely remembered for Strawberry Hill, the home he built in Twickenham, south-west London where he revived the Gothic style some decades before his Victorian successors, and for his Gothic novel, The Castle of Otranto. Along with the book, his literary reputation rests on his Letters, which are of significant social and political interest. He was the son of Sir Robert Walpole, and cousin of Lord Nelson."