Examples: directions and locations I

Here are sentences from the dialogue. The first one tells us where something is located:

Auf dem Berg gibt es eine Skihütte mit einem Café.

Where is the ski lodge? On the mountain. Auf dem Berg.

The preposition used is "auf" and the case used is the Dativ "auf dem Berg", the article "dem" is in the Dativ case. So, the rule is: If you can ask the question "where", in German "wo", then you should use the Dativ case with the preposition.