"How Nuth Would Have Practised His Art Upon the Gnoles" by Lord Dunsany

There's another reference to Slith! (See: "Probable Adventure of the Three Literary Men" for the reference)

Belgrave Square is a real place in London! It dates to the early 19th century, and is located just a little bit west of Buckingham Palace. Fancy!

The picture used is an illustration by Sidney Sime in the 1912 edition of "The Book of Wonder".

To follow along: https://www.gutenberg.org/files/7477/7477-h/7477-h.htm#HOW_NUTH_WOULD_HAVE_PRACTISED_HIS_ART_UPON_THE_GNOLES