Learn German: Was für eine Minibar ist das? - What kind of minibar is that?

The phrase was für ein- (what kind of) changes its ending to match the gender and case of the noun it goes with. Here, it goes with Minibar, which is a feminine noun. Because the verb is ist (from sein, meaning "to be"), the noun is in the nominative case. The feminine nominative ending is eine.

Doesn't the word für normally force the next word to be in the accusative case?

Usually, yes! The preposition für almost always takes the accusative case. However, was für ein- is a special fixed phrase. In this phrase, für completely loses its normal rule. The case of ein- is decided entirely by its job in the sentence, which is nominative here because of the verb ist.

If Minibar is feminine, why does the sentence end with the neutral word das?

When pointing something out or identifying it (like saying "That is..." or asking "Is that...?"), German uses the neutral pronoun das, regardless of the noun's actual gender. You would use the feminine pronoun sie to say "It is small" (Sie ist klein), but to ask "What kind of minibar is that?", you just use das.

How can I remember that Minibar is a feminine noun?