This at the museum thingie outside where the rebels are shooting striders (after the bit with the floor turrets you throw grenades down). You have to go through a little tunnel between 2 large blast holes to get to the street, they're by the wall where the rubble falls down when you first try to...
Argh I thought I'd seen the last of those on the continent!
I killed someone with a sink today, it bounced off the floor and killed him but it counted as him committing suicide. Also, if you fire an object as close to vertical as you can then run forward and get hit and die, you sink through...
Just get to the top where the portal opens and gunships come out, then grab the energy balls up there and shoot the gunships, then shoot the bit at the bottom of the massive portal where metal shields will appear, break off when you hit them then you shoot where the were and your done.