Where in Duluth?

I don't know, but it looks like some serious skateboarding to me.

That's in Gary over by Stowe School ... 102nd Avenue West?

I have no idea what they are used for.

I beleive, this is the cement blocking what was the drive way to the origional Fryberger house.  It's off Cloumbus Ave. Final answer, Alex.

Looks like a boat cradle to me....was it from the viking ship on the lakewalk?

Not sure where it is, but it is the cradle for a large LP tank.

D_mauling, you are mostly correct - it's on South Carterret Street...

I honestly don't know what it is... I figured some remnant of some kind of pipe system.

I win the bonus points because I know what it is.

Pretty sure that was a cradle for the pipe that carried molten lead and PCBs down to the river.

@Topofthehillman: The Fryberger estate has proper brick and wrought-iron gates.