Attack of the giants, tower and white cold (The Witcher 3: Wild Hunt)

I tried to find a topic about what was happening at the end but did not find it.
So, what happens at the end, after defeating the king of the wild hunt? What kind of elven tower is it and what is it for, where do the crowds of ice giants come from, and what is white coldness?
First, let's deal with the tower, most likely it serves as a signal amplifier for interdimensional movements or is a kind of place of power, which in general does not really change the essence. But where the ice giants come from, it is not entirely clear how much is known at the first conjugation of the spheres, many creatures penetrated the world, and here only they. If we assume that Ciri opened a portal to the source of the white coldness, it is very likely that the giants inhabit the area where the source of the white coldness is located, or, in extreme cases, the worlds associated with it. This implies two conclusions, firstly, not such a deadly white coldness (well, or at least not for everyone), and secondly, this is most likely a natural phenomenon, and not someone's malicious intent. Continuing the theme of white coldness, according to the assurances of some characters, he is nothing more than death for any world and his arrival is inevitable. And how does it actually come, does it happen somehow naturally or as a result of careless handling of interdimensional portals? Judging by the worlds in which it was observed, this is a local phenomenon affecting only the surface of the planet, and not something spreading through the cosmic vacuum, since the sun continues to shine with normal intensity. So what did Ciri do, just plug the hole where this white cold was coming from? And what is all the same, this "white cold"? this is a local phenomenon affecting only the surface of the planet, and not something spreading through the cosmic vacuum, since the sun continues to shine with normal intensity. So what did Ciri do, just plug the hole where this white cold was coming from? And what is all the same, this "white cold"? this is a local phenomenon affecting only the surface of the planet, and not something spreading through the cosmic vacuum, since the sun continues to shine with normal intensity. So what did Ciri do, just plug the hole where this white cold was coming from? And what is all the same, this "white cold"?