Having just started a new game, I fully intend to build myself an Arena for the eventual Eye of Cthulhu fight, and naturally an equally elaborate arena for my Eater of Worlds and Skeletron fights to come.
Bearing in mind that the latter two will be in pre-determined locations (Corruption and Dungeon Entrance, respectfully), how can I optimize my arena construction?
Ease of movement against bosses, as well as suggestions for elegant decorations that won't spoil the utility of these areans, are welcome.
To start things off, I'm aware that a major component of my arena should be platforms that are well-spaced to my jump height, and ensuring it is closed-off from wandering mobs who might encroach upon the battle. Though preferably, I'd like to open it up for eventual Goblin Army Invasions.
Best Answer
Terraria.gamepedia.com has example arena structures for several bosses.
The general idea is to make a screenwidth area with a completely flat floor and usually at least one platform to jump on, or a tower of equally spaced, long horizontal platforms for floating enemies like Skeletron or the Eye of Cthulu to avoid their attacks better. Material doesn't matter other than the floor should be solid and you should use wood platforms for the other sections so you can jump up/down at will. Walls are rarely useful for arenas so leave them off unless there's some reason you need/want them. Note that the Wall of Flesh will need a much much longer arena (a straight platform really) than other bosses.
As far as decorations just use anything you want that's a background later item (like beds, torches, anything the player walks over). If it doesn't obstruct your movement it doesn't get in the way.