Why not walk?
Some time ago I came across this interesting website - Walkit. At first, it only covered London, but now it includes other cities as well - Birmingham, Edinburgh, Newcastle & Gateshead, Leeds, Derby, Aberdeen and Glasgow.
All you have to do is put in from where you are starting your walk to where you want to stop and it gives you a lot of details on how to get there including a map, as well as other interesting facts such as distance, how long it will take you to reach the destination, calories burnt and CO2 avoided!
As stated in their website, they want to get people walking more. They think that walking in and around town can often be a smart choice. No timetables to keep to, no journey delays, no overcrowding, healthy, green, free, direct, access to services (and sunlight!) en route.
Obviously one cannot substitute walking for all the urban car/bus/taxi/tube trips one makes. But the website will at least help one make more informed decisions about whether they choose to walk for all, or part, of any given journey.