Food is usually on sundays, from 7pm. It's very cheap, but the place is not just about the food. This is not a restaurant, but a people's kitchen. You'll meet very interesting people here. Also, this is a good place to connect to the left-wing student scene in Heidelberg. This place might not be for everyone, but if you're open minded and inclined to get to know people, give it a go.
Cons: not exactly clean, food quality varies