Next to the Alnatura chain, Füllhorn (Fuellhorn) is the "other" organic store in Karlsruhe, but this one is located right in the city centre.
They differ in their offerings mostly in terms of what brands of foods they stock. Both are worth checking out!
Note that Füllhorn does not accept credit/debit card payments below a certain amount; it used to be 20 Euro if I remember correctly. Make sure to carry enough cash!Pros: location, veggie selection, friendly staff
Cons: credit/debit card handling