Tokyo, Osaka, Kyoto and Nara?

Tokyo, Osaka, Kyoto and Nara:
How easy to acess by train and then on foot. I have heard taxis are very expensive.
Also, from the 3 larger cities, what are some day trips not to miss?

Access and orientation pages for...

... Tokyo:
http://www.japan-guide.com/e/e2017.html

... Osaka:
http://www.japan-guide.com/e/e4006.html

... Kyoto:
http://www.japan-guide.com/e/e2363.html

... Nara:
http://www.japan-guide.com/e/e4107.html

Also, from the 3 larger cities, what are some day trips not to miss?

See here (2 dots means "best of Japan"):
http://www.japan-guide.com/e/e623a.html