Transport for London are offering rare walking tours through the London Overground Thames Tunnel this weekend, while trains are suspended for engineering work.
The £18 ticket cost will go to charity - but all 4,000 sold out in just 4 hours.
The tunnel was constructed in the 18th century, and it's only the second time in 150 years it has been open to the public.
He's starred in more than a hundred films and won dozens of awards including two Oscars. Sir Michael Caine has come a long way from his humble beginings in Southwark but today he was back in his home borough, along with some other high achievers, for a very special occasion, Liz Wickham reports.