Photo:
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Juggzy
Historical version 4 of Category Waterloo And City Line (view current version)
The least complex Tube line of them all, the Waterloo & City Line (also known as the Drain) has only two stations. It's primarily used by commuters, and hence doesn't run at all on Sundays or late evenings.
See also:
Stations on this line (view them on a map):