London (CNN) - Queen Elizabeth II is to head below ground Wednesday with Prince Philip and Catherine, Duchess of Cambridge, to mark the 150th anniversary of the London Underground.
The royals are visiting central London's Baker Street station - a stone's throw from the home of Sir Arthur Conan Doyle's legendary fictional detective Sherlock Holmes at 221B Baker Street.
The queen was forced to cancel some visits last week because she was experiencing symptoms of gastroenteritis.
Once below the surface, the royal party will view a restored underground coach dating back to 1892 and talk to the people involved in bringing it back to its former glory.
CNN's Max Foster reports on the Queen's first public appearance since her recent hospitalization.