Learn Polish: Supermarket jest obok banku. - The supermarket is next to the bank.

The preposition obok (next to) always requires the noun following it to be in the genitive case. For a masculine inanimate noun like bank, the genitive ending is usually -u, making it banku.

Do other location words behave like obok and force the genitive case?

Yes! Many prepositions of place require the genitive case. Common examples you might know include blisko (near), niedaleko (not far from), and naprzeciwko (opposite).

Why doesn't supermarket change its ending like bank did?

Supermarket is the subject of the sentence because it is the thing doing the action (in this case, just being). The subject always takes the nominative case, which is the basic dictionary form of the word.

Could I say Obok banku jest supermarket instead?

Yes, you can. Polish word order is flexible. Putting obok banku at the beginning puts slightly more focus on the location, answering the question of what is next to the bank. The original sentence focuses on the supermarket itself, answering where the supermarket is located.