What to see/do in Nottingham?

Any advice on what to see/do in Nottingham?  I'm going there 10th June to see a photo exhibit and was wondering if there's anything else to see/do while I'm there.  Thanks.

There's an IKEA there. That's all I know of 

There are loads of shops and two malls within a do-able walking distance from the train station.

The Castle is interesting - it's not really like a castle, more like a big old house, but it's on a huge rock with good views - there is also a great pub just below the castle - also, go visit the Lacemarket - a network of old streets with little shops and cafes - all in the city centre - there is a good tram network too to get you from the train station - Nottingham is a good place at night too - I've found it to be pretty relaxed and friendly - try the pubs along the canal.  Have fun!

PS - don't go to the Robin Hood museum - it is NAFF!

Thanks everyone for your replies.  The photo exhibit I'm going to see is actually at the castle so it's good to know that it's worth checking out.  It's funny because Nottingham isn't very far from Birmingham, yet when I asked advice at work not a single person had ever been there.