Hola Emanuel
We are using the indicative in this case after aunque to express something that the speaker considers "a new piece of information" or simply "wants to state this piece of information as a true one". It is as if it was a confirmation of what he/she believes. He/she is making a point about that.
However I understand that this could be taken as "shared" by everyone, because it is a universally known fact, (everyone knows Paris is beautiful) therefore triggering the subjunctive, as you were saying.
So, this sentence could have been said in two slightly different situations:
1. It is something that everybody knows, it is obvious, but the speaker is determined to state it as a true fact. This is reinforced by the use of indicative.
2. The two speakers have already being talking about how beautiful Paris is, so they've shared this information and agreed on it. So if this bit of information is repeated in their conversation again, the subjunctive would be used, as they have shared this previously. It is something that is known and accepted by both "Paris is beautiful".
I hope this clarifies it for you. There are little nuances in Spanish when using "aunque". We are aware that "aunque" is a complex connective and we will be extending the content related to this in the future in Kwiziq, to make sure all these nuances are understood by the students.
Gracias y un saludo
Inma
