Moat Cailin, once an imposing fortress built by the First Men, is now almost completely in disrepair. Of the 20 original towers, only three remain while the rest of the fortress lies in ruins. Situated at the most important strategic position between the North and the rest of Westeros, Moat Cailin is extremely important in times of war.
Frankly, I'm surprised that someone hasn't kept the place in better repair over the years - given its strategic importance.