Liverpool Street and Moorgate.
Some years ago a work colleague of mine, who didn't know London very well, had to go to offices in Broadgate (next door to Liverpool Street on the old Broad Street site) and having arrived in Euston, walked over to Euston Square to pick up the Met / Circle to Liverpool Street. When he told me this, trying to be the helpful work colleague, I suggested next time he simply pick up the Northern Line at Euston and alight at Moorgate, which he duly did and then walked to the Met platforms to go one stop to Liverpoo Street... I happened to meet him at Broadgate and laughed when he told me what he'd done - when we left the office I showed him why I'd laughed, come out of Broadgate, turn right, walk 2 mins along Eldon Street and you can see Moorgate station......