What's the Kennection? #57

In what city could you visit the graves of Francis Scott Key's son and Edgar Allan Poe at Westminster Hall and Burying Ground?

What did Kristen Stewart and Robert Pattinson do in four Twilight movies that won them four straight MTV Movie Awards between 2009 and 2012?

What Eric Clapton-led group recorded Wheels of Fire, the first platinum-selling double album?

On December 31 of what year did the United States return the Panama Canal to Panama?

What two gems, in order of abundance, make up 99% of the bling on Queen Elizabeth's crown?

What's the "Kennection"?