In message , Jarle H Knudsen
writes

If, when visiting London as a tourist in August, I should like to ride one
of the underground lines in its entirety, which line and branch would you
suggest, and why?

In addition to the excellent suggestions from others, it is worth taking
a look at Baker Street, one of the oldest of all "underground" stations,
where the Circle/Hammersmith & City platforms have been restored to
something approaching their original appearance - given all sorts of
modern operating restraints.

Also, if your definition of "underground" is broad, then take a ride on
the Docklands Light Railway from Bank out to Greenwich (Cutty Sark). If
you position yourself right at Bank you can sit at the front of the
usually driverless trains, in a "driver's eye" position" and enjoy the
very steep climb from deep-level Bank to above the rooftops as you join
one of the oldest viaducts in London - then enjoy the spectacular views
of Docklands before plunging under the river to Greenwich.

After seeing the sights, return to central London by River Bus if the
weather is good - or double-back to Canary Wharf and then enjoy the
spectacular modern architecture of stations on the Jubilee line on your
return trip (it is well worth getting out at most of them, up as far as
Westminster, if you are keen). I've lived in London for more than 50
years and I still find this one of the most enjoyable trips when showing
visitors around.

--
Paul Terry