The walls sorrounded once the entire city, now they are in different stages of decay, but the have an opeing for the cars to pass through
Kano is a very attractive and busy place in the North of Nigeria.
The Durbar festival which take place twice a year during the Muslim celebration of Id-el-fitr and Id-el-kebir is a very good opportunity to go and visit Kano.
Not the greatest looking mosque but a very important one that gathers up to 50,000 people for prayers. Right in the same area there is a good museum and the Emir's Palace.
These are a fun way to get around the city. The drivers are nuts. It was a blast going down the wrong way of the street dodging traffic. They are all over the city and are cheap to hire. Becareful though, accidents do happen. A car hit us when I was on one of these motorcycle taxi. It wasn't that bad but the danger still remains.
Kano has a fairly strict Muslim society. When I was there I saw a lot of Osama Bin Ladin propaganda posters and I was talking with some shadier characters as in the more fundalmentalist type. I had no problems and you should not have any also if you respect the Islamic ways.
Favorite thing: There are a couple of big flat hills in Kano. It is possible to go to the top of these hills and get a good panoramic view of the city. Great for taking pictures.