Dans or à la for in
The bottles are in the cellar. I put Les bouteilles sont dans la cave. It marked my answer wrong and said it should be à la cave. Then later it had a sentence as Mon vin est dans la cave. My french teacher said she didn’t know of a rule about this and that using dans for the Les bouteilles sont dans la cave should be correct.
I have a bottle of wine right now, in my hand, that I'm looking at. (I went down to the basement and got it when I read your question.) It clearly states "mis en bouteille dans nos caves" on the back label. So I'm going to conclude that your teacher knows her stuff.
. Merci. So that means duolingo was wrong! I often will click on the “my answer was correct” when they have something like that, but I never see an explanation.
So à la cave is a little more general. Like you say je suis à la maison. It could mean you are inside the house or around the house. You could be standing on your porch.
So where do you keep the wine?
À la cave.
D’accord. Je suis à la cave mais où exactement est le vin?
Dans la cave.
Are you sure there wasn't another mistake in your answer? I am going through that section right now and I get that phrase very often and I always translate it as "Les bouteilles sont dans la cave" and it is marked correct.