I live in London and for commuting around via public transport OR walking I always use Citymapper, which is massively superior than Google Maps for directions. I suspect they are using Googles APIs underneath it all, but their UI is better than Google maps and also their recommended public transport directions are orders of magnitude better than Google Maps.
Citymapper will get you between any two locations in London and give you many options based on cost or time or preference for one transport type (e.g. preferring tubes versus buses). Citymapper also gives multi-modal directions: e.g. walking PLUS take an Uber. Or walking, tube, then a cab. Not only this, but it ALSO tells you where you should sit on a train so you have the least walk when you exit the train.