I just finished the first season of "Game of Thrones", where one of the main themes is 'The Wall', a huge ice wall that devides the realm (Westeros) from the dangerous and winterly North.
From what I could gather this huge construct is not man-made. It was mentioned that it simply rose a few hundred years back from the ground. One of the characters says this when mentioning that they were no different than the wildlings, just happened to be on the right side of the wall. EDIT: found the quote on IMDB:
Tyrion Lannister: But... I don't believe that giants and ghouls and white walkers are lurking beyond the Wall. I believe that the only difference between us and the wildlings is that when that Wall went up, our ancestors happened to live on the right side of it.
Apparently the northern side of the Wall is extremely dangerous, hosting wildlings, dangerous animals and the mysterious "White Walkers". Therefore, the Night Watch has to constantly guard and protect the Wall from outside dangers.
What I don't understand though is: Where does the long tunnel leading through the Wall come from?
It is featured in the very first scene of the series, definitely looks man-made (it's shaped in a perfect bow form) and is covered by multiple massive gates.
Did the people from Westeros cut the tunnel into the ice? It would've certainly taken years to do this.
And if yes, what motivation could they possibly have? They probably knew before the wall came up that the north was dangerous. Why would they undertake such an effort to open a passage to this risky area?
Apart from just being not of any worth to them, it also leaves a gaping hole in the otherwise perfect defensive structure that the Wall poses.
Considering the risk they would certainly be better off to close the tunnel than to have a passage open and constantly send patrols out there. And even if they needed to go north of the Wall, they could simply let themselves from above, couldn't they?
So is the tunnel man-made and with what motivation, or is it simply a story device?