|Central Line:||west||Tottenham Court Road||Holborn||Chancery Lane||east|
|Piccadilly Line:||west||Covent Garden||Holborn||Russell Square||east|
Holborn Station is the only interchange between the Piccadilly Line and the Central Line, replacing the earlier British Museum Station in 1933. This explains why it doesn't have central platforms like many Central Line stations.
Holborn has four (long) escalators from street level to an intermediate level. From there, you turn left to the Central Line which is down a staircase or right to the Piccadilly Line, which is down escalators; for the northbound line, you pass under the other lines and climb up to the platform level.
There's a hidden platform up some stairs behind a locked gate at the front of the westbound Piccadilly Line platform. This used to be the end of the Aldwych shuttle, which closed in the 1990s. The track is still intact and used for film shoots.
For Piccadilly Line exits, the best place to be is toward the front of westbound trains or the back of northbound ones; for the Central Line, it's about 1/3 back on westbound, and 2/3 back on eastbound.
Piccadilly line westbound, go to the right-hand side of the platform to be at the less-crowded back of the train. To be honest, at rush hour I'd say walk to Russell Square instead; you're much more likely to get a seat there and it's less than 10 minutes' walk away. At peak times, the number of people entering the station is restricted, so you'll see queues outside the station.
There are no facilities inside the station, apart from a cashpoint just outside the barriers, but there are lots of sandwich shops around, and there's a Sainsburys opposite. In the evenings, there's sometimes a man selling hot dogs. This evening I saw a man outside selling roast chestnuts, but I was in too much of a rush to buy any. [Coffee Matters]? is good, and close, but only open in the day.
I read on (void) that the Wimpy is now a Burger King. --Kake
Hence the Wimpy website doesn't list a restaurant at Kingsway I think it's save to say, that the Wimpy is indeed now a Burger King. --KaiMichaelPoppe