November 29, 1898

The Whipsnade Zoo is large, 600 acres, and one of the major conservation zoos in Europe. This zoo is 30 miles north of London, and one of two zoos run by the Zoological Society of London. In 1931 the zoo had only been open to the public for some months. I don't know if C. S. Lewis saw any lions the day he and his brother visited there in September of 1931, but that seems a sensible conclusion. C. S. Lewis (November 29, 1898 to November 22, 1963) says this about that day in his book, Surprised by Joy: The Shape of My Early Life (1955) :

“When we [Warnie and Jack] set out [by motorcycle to the Whipsnade Zoo] I did not believe that Jesus Christ was the Son of God, and when we reached the zoo I did.”

Mind you Lewis was already a theist with an active prayer life when this conversion happened...The compilers of a chronology of Lewis's life give us  a pleasant read and one available at cslewis.org.

The chronology does not dwell on the reasons that Lewis and his brother moved in with the mother of their friend who died in the war.  But they all lived together after World War I ended, for the rest of their friend's mother's life (1951). I guess the reason is obvious.