Answer:
I think the answer that best fits to the question would be "Das ist ja fantastisch" (that is fantastic)
It could actually also be "Sehr schön" (very nice/very beautiful), or "Das ist schön" (that is nice/that is beautiful).
But I personally would say the first one is correct.
It is DEFINETELY NOT "Das ist kühl", because that just means "That is cold", and that has nothing to do with that.