If we replace the conjunction ‘although’ by ‘in spite of the fact that’, it might be easier to shed some light.
In spite of the fact that she was not feeling well, she went to work.
In spite of the fact that they had never seen the ocean, they had heard about it.
The second sentence, so far, has a similar structure to the first. Now, the author wanted to add a reservation (a ‘but’) to its second clause: (…they had heard about it,) but never seen it.
We could also do that to the first sentence, e.g.:
In spite of the fact that she was not feeling well, she went to work, but couldn’t really concentrate.
I agree with Conchita’s take on using although and but together in a sentence. But I would also be interested in seeing the complete sentence(s) that your Indian author wrote prior to writing “Although they had heard about it, but never seen it.”
"A long time ago there were people living high up in the mountains. They had never seen the ocean. Although they had heard about it, but never seen it, and this made them feel very sad. So one woman in the village said, “Don’t be sad; what you can’t see, you can see–you just have to see without looking…”
Tom
PS: Amy, does it seem OK to you? What if I remove “but” from the sentence? What about spoken English–I mean, would it sound odd even in spoken English?