Here are some of the awesome set pieces and magical effects from A Song of Ice and Fire (a.k.a. Game of Thrones) written up as hermetic spells for Ars Magica. This particular post is all about “The Wall“.
The Wall is reported to be over 700 feet tall and is made of solid ice. It was supposedly constructed using both magic and mundane means some eight millennia ago, in the aftermath of the Long Night to defend the realm against the White Walkers who apparently dwell in the far north, though they are now considered myths by most.
Source: Game of Thrones Wiki
Aside – when your GM says “these creatures are thought to be a myth” you should expect to gear up to fight them; its a pen and paper rpg thing.