About Carcassonne, yes do the walk around the winding streets at the castle. Yes it is full of tourist crap and restaurants with pictures on the menu (beware!), but if you are there, it's what you do.
If you will be in Carcassonne for a few days, go to the main town outside the citadel called the Bastide St. Louis, it is a great vibrant place, walk around, some lovely independent shops and a great market in the Place Carnot (check market days), lovely bistros and restaurants all around there, and much used by the market folk and locals, which is where the real deal is.
If you have time, take a train (short hop on the local train) to Limoux, another dreamy place where the main activity is lazy boules on the pitch followed by wine in the local shops, as there are lots of vineyards and wineries around. A favourite is Cremant de Limoux and you can get a free taste if you take a stroll outside the town to one of the wineries.
The walks along the Canal du Midi are gorgeous with the lovely shady trees. I took a barge trip, but you have to make sure there is English spoken (unless you don't care and just want to enjoy the ride!) and it was so relaxing and peaceful puttering along at a nice slow pace.
So there, you will enjoy Carcassonne if you explore outside the castle area, enjoy!