Someplace safe to blow things up. Well, this was going to be as close as they could get. Lina'd had a portal to her world, one that led to a house on a lake. They weren't going to be casting anywhere near the house, oh no. Instead, there's a floating bridge out to the center of the lake, and a platform there. See? This way, it is very unlikely that things will get set on fire too much.
But it's a fireball spell! Definitely it will require some things getting set on fire!