The OP hasn't come back with any further insights, so, in the unlikely event that he enjoys cycling, then my preferred method might be of interest . . .
I'd take my bike on the train to Kings Cross, leave by the east (York Way) exit and carefully cross the one way road before pedalling south down Greys Inn Road and following the Thamelink route cross the river at Blackfriars Bridge then follow the south bank cycle routes to Greenwich, or else, stay north of the Thames by a zig-zag east onto Clerkenwell Road then south thru Aldergate before the high point of cycling along the breathtaking landscape of London Wall, the quaint Wapping 'Highway' of old warehouses and then through the murky Greeenwich foot tunnel.
Clearly this isn't for everyone, but it can be quick, safe, simple and highly interesting (and also costing nothing), and if the OP has the time, inclination and interest, then the visible history along these routes will be unforgettable.