It's a lil place with great food and reasonable prices that is running up against the established fast food chains. With locally sourced ingredients, a homely feel and of course, their 7 different burger creations they have established quite a large number of followers. That being said, prepare to queue up when you come at peak hours.
derfreiBurger is right in the middle of the old town and makes for the perfect quick lunch stop when exploring the city. If you're on a budget you don't have to eat less good as their burgers range between Eur4.50-6.40. They also have a vegetarian burger and hot dogs but are popular for their Cheeseburger, the Texas Bacon Burger and so on.
Try the BBQ Bacon Burger with their homemade sweet bbq sauce and fried onion rings (Eur5.80).
Mon-Sa: 11:30-21:00