The arena shall be a place called the Howling Abyss. It kinda looks like this:

[img]http://img2.wikia.nocookie.net/__cb20130325214058/leagueoflegends/images/thumb/a/a8/Howling_Abyss_concept1.jpg/500px-Howling_Abyss_concept1.jpg[/img]

Essentially it's a long bridge over a very deep chasm, in a wintery land.