Underground
The railway station is so complex and huge that’s it’s hard to give exact directions to the tube. ‘Follow the signs’ is not helpful. There are so many entrances and exits and a big shopping arcade downstairs on the way to one tube entrance.
The Northern line takes you south to Battersea Power Station, Clapham and Morden, or north to Euston, Camden Town, Highgate and Hampstead.
The Jubilee line goes east towards the Docklands area (many hotels there) then north to Stratford, good for interchanges, including the Central line and DLR. West it covers many popular areas: Waterloo, Westminster, Green Park, Bond Street, Baker Street and north.
Distances to the platforms and for changing between lines are quite long with lots of steps.
It’s also not so far (five minutes maybe) to walk across the actual bridge to get to Monument for the Circle and District lines, if that is easier for you.