However, recently I found myself at BlackFriars Station (southeast Circle (yellow) Line) and discovered it was closed. Knowing there are Tube stations scattered all over the city, I started walking north, only to find myself at Farringdons Station (northeast Circle Line). They don't to look to me to be that close on the Tube map, but a fried pointed me a geographically accurate Tube map. Those stations, despite being on opposite sides of the Circle Line, are actually quite close together.
What a fun city.