Search london history from Roman times to modern day
A bit out of date, but this interactive map of step free London is very good
All the London railway stations :
Underground lines : Bakerloo, London Overground (Watford DC Line), ThamesLink
Accessibility friendly : Nearest National Rail stations with step free access are London Euston and Harrow & Wealdstone. Wembley Cental is not accessible to wheelchair users due to stairs between the platforms and street level.
General description : See wiki
More comment : National Rail Map & Guide, 32 steps to platforms.