To add to abmj-jr's solid response, the area just around Nippori station is one of my favourite districts in Tokyo.

There are three areas that make up what is popularly known as YaNeSen.
There are lots of websites with information and suggestions for walking tours - use Yanesen as a search term and Flickr will yield a lot of results also which will give you an idea of what to expect
http://en.japantourist.jp/view/a-day...anaka-in-tokyo

There's a travel writer (best when writing) I've come to respect who covered this same area in his own 48 hours in Tokyo guide.
http://m.youtube.com/watch?v=9Qc8bs3...%3D9Qc8bs3oXJM
The coverage is here - scroll through to the 6 minute point for a short guide. I second the recommendation of the udon restaurant he visits (my husband used to work regularly in this area which is how I got my own introduction)