If you can get a copy of Champions Battlegrounds (5th Ed.) there's two places that might suit your needs--a shopping mall and an amusement park. Both have plenty of innocent bystanders to endanger, plenty of items to use as improvised weapons--and in the parlance of video game design, fully destructible environments.
Any sort of convention or trade fair would be a good place for a super-battle. Again, we have innocent people to endanger and items to use as weapons--and if it's a comic or sci-fi con, we have cosplayers who might decide to try their hand at superheroics. (It doesn't have to be sci-fi or superheroes, either. Check out the schedule for the Donald Stephens Center for some show ideas.)
On a related note to conventions--a gun show has tremendous potential for chaos and catastrophe, especially in states that permit open and/or concealed carry. In any other situation a criminal suddenly faced with dozens, if not hundreds of armed individuals would be strongly inclined to surrender--but if that criminal was Bulldozer, or Holocaust, or someone like them, not so much. The potential for collateral casualties would be especially high.
Hope that helps.