The White Walkers have been these mysterious ice zombies who want to take over Westeros for almost five seasons. And that’s all we’ve known about them. They have just been wandering North of the Wall though their army has increased over time and they have taken over certain places like Hardhome but nothing substantial has occurred as of now or till episode five, ‘The Door’. We know that the Wall has magic spells on it, just like the Three-eyed Raven’s cave and that has prevented the White Walkers from crossing it till now. However that might not be the case anymore and the reason as it looks like, is Bran. Bran is going towards the Wall and there are high chances that he will cross it and that’s where the problem arises. In the recent episode of Game of Thrones, we came to know the protection covering Three-eyed raven’s cave could be(and thus, was) broken by the mark the Night King gave Bran during one of his visions.
There is a character named Coldhands in the books though he might not appear on the show, and he explains how the Three-eyed raven’s cave is warded from White Walkers. In the books, he is the one who escorts Bran, Meera and company to the Three-Eyed Raven’s cave and there is an excerpt which goes,
“Inside the cave?” suggested Meera. “The cave is warded. They cannot pass.” The ranger used his sword to point. “You can see the entrance there. Halfway up, between the weir-woods, that cleft in the rock.“
“What about you?”
“The cave is warded.”
So White Walkers could not enter the cave due to the magical protection that the Children of the Forest have put over it. But that was only till the time Bran was not given that mark by the White Walkers. Now, going by this, it can be deduced that the reason they haven’t yet tried to enter Westeros is because of the Wall. George R.R. Martin at some point said that, “more than ice went into the raising of the Wall. Remember, these are fantasy novels.”
Going back to the history of the wall, its generally established that a Stark named Bran (the builder) had erected the wall with the help of Children of the Forest with magical spells. So it can be deduced that the same spells existed on the Three-Eyed Raven’s cave and that got messed because of the mark Night’s King gave Bran. So if Bran crosses the Wall with Meera, then White Walkers might be able to get through the Wall or might even tear it down!
However, even if the White Walkers cross the Wall, there are few places in Westeros which could never be raided by White Walkers. One of those places is Storm’s End, which is the seat of House Baratheon, where Melisandre took Ser Davos to deliver the demon baby to kill Renly Baratheon. She says, “This Storm’s End is an old place. There are spells woven into the stones. Dark walls that no shadow can pass – ancient, forgotten, yet still in place.”
Apart from Storm’s end, there is another place which has this magical touch and that is the Stark home, Winterfell. In the books, Tyrion Lannister says that, “There had been a great strength in those stones, a sense that within those walls a man might feel safe.”
It’d be pretty interesting if White Walkers fall in Winterfell or at the Storm’s End. This will also be a fitting end to the show but before that we need to wait for Starks get their house back from Boltons.