That is not a bar. It is a stack of mortar joints with a top on it. Plywood the floor if you're saving it and go at it with a sledge.

That sounds like good news! What do you mean by plywood the floor?

Put down Plywood, moving blankets, and 6 mil plastic, to protect the floors. Move all the furniture out. Now whack it.

And wear good eye protection if you are wrecking it with a sledgehammer.

If you were my neighbor I would beg you to let me demo that for free.