Hokkaido is the northernmost of the four big islands that make up Japan. It is really a great place if you are an outdoor enthusiast. There are many many hiking possibilities in the great national parks such as Daisetsuzan and there are some good skiing slopes (Sapporo hosted the winter olympics once).
Sapporo is the capital and one of the most lively cities of Japan. It has a great beer drinking culture. The city is an ideal place to arrange everything for a trip to some of the most remote parts of Japan.