I would translate your sentence with: Es muss da/dort einen Keller geben.
Ein Keller muss da sein, is a sentence I don't really understand without pronounciation. Does it mean: "A basement must be over there (at that place)" or just "There must be a basement (somewhere)."
If in doubt both are right. Yours is somehow a mixture of both meanings, maybe report the sentence as a whole. It is confusing.
I hope I could be of help.
The thing is "da sein" is a way to express existence. "das Dasein" = "the existence". "Es muss da sein." is normally meant as: "It is needed." You use such a sentence if you are looking for a new apartment. e.g.:
"Good flat, I like it. It doesn't have a basement though." - "That's no good There has to be at least a basement!(It does need at least a basement!)" = "Gute Wohnung, sie gefällt mir. Allerdings hat sie keinen Keller." - "Das ist schlecht. Es muss schon mindestens ein Keller da sein."
Or you might use this sentence, if you are searching for something:
"I can't find the keys. Are you sure you haven't lost them?" - "Just keep searching. They have to be here. (I need them to not be lost.)" = "Ich kann die Schlüssel nicht finden. Bist du sicher, dass du sie nicht verloren hast?" - "Such einfach weiter. Sie müssen da sein."
It is also possible to put a lot of emphasize on the "da". Then you might use it when planning a building.
"Ich würde die Keller nach dort und dort bauen." - "Unsinn. Ein Keller muss da sein." - "I would build the basements there and there." - "Nonsense. One basement has to be (over) there."
Problem here is missing context and missing pronunciation. Some extra words might also help to identify how the sentence is meant. It's just the "da" here doesn't necessarily point to a specific location. Because of the "must be" you could understand that the location is not known. The "da" would therefore be a rather vague location.
I hope I could be of help.
For me, the English answer "The must be a cellar" does not convey useful information unless there is additional context, either a gesture that would imply location and hence "there" or sentences that set the context of this one, e.g set in a paragraph about a particular building. If the context is provided then the use of here or there in the sentence makes sense.
Yeah, I think you're correct. According to this link, http://www.dict.cc/deutsch-englisch/da.html , "over there" is shown as a translation to "da drüben".
"Da" alone would be "there".
The same appears in others sites I looked up. Now, thinking again about it, it doesn't seem just a big deal. I mean, it is something we can tell by the context. But it is just me, guessing...
This sentence is easy: modal verb takes second place, the other verb last place. So knowing that, you can now say ein Keller muss da sein where we emphasise the cellar, or da muss ein Keller sein, where we emphasise that the cellar must be there.
These are the very basics, but I find this page a good resource:
Take a look at the TeKaMoLo rule, I think that's the trickiest part. I was totally confused until I learned of its existence.
My typo worked for me with "A basement must be here" (i noticed the missing 't' at precisely the moment i tapped the button to check my answer) i was seeing it as "keep looking i know this is the house and i distinctly remember being dragged down damp stairs and kept in a dark musty room. So rip up the floor boards i don't care. There must be a basement.