Campus Lounge is a cool place just next to Kassel's university. It offers several cool cocktails (although not too strong ones, the "Zombie" I had didn't turn me into a zombie, so it was rather weak!!!) and great food! Be prepared for a nice bar that doesn't resemble a lounge, but still is a great place to hang out at night.
A great thing is the Happy Hour which is strategically set from 20.00 to 21.30 - a time where all other bars don't have a happy hour. During that time, all cocktails in Campus Lounge will cost no more than 3 Euro.
Dress Code: none
The Cook is a relatively new theme bar in Kassel. Everything is about travelling on the seven seas (Cook is the name of the guy who discovered Australia for the world). That's why you sit on a ship-resembling terrace and get your drinks served by sailors...
Dress Code: no dress code