Arenas

I was just wondering,how do you get into those arenas in amnoon desert and the koga arena?There are big gates sealing the entrance.

u go to competition arena, and u will end up there.

All level 20 random arenas are accessed via the Lion's Arch arena, head to the docks and you'll find the arena guard there. When you enter the arena, unlike Ascalon and Yak's, there will be a different map every time because they consolidated all the maps into one.