In article , ..@.. (Q) wrote:

To change between the District and Circle lines and the Central or
Northern or Waterloo & City lines, exit Monument station and follow
the signs above ground via King William Street. If you are using
and Oyster card, please touch in and out as usual. You will not be
charged twice."

If, however, you are on a National Rail outside London to Zone 1 (or other
zones) ticket you won't be let back into the station. BTDTGTTS.

--
Colin Rosenstiel