Someone grabbed this POD from QJ (not sure if that requires "permissions" or not), put it on Facebook Quetico Group page, & raised the same question.  Most guesses had to do with bridge &/or pier base supports.  Someone indicated they've seen similar structures in the BWCA and over in the LLC area (or maybe it was Crane Lake, can't recall exactly). I didn't read all the comments but those first few guesses seemed fairly reasonable.

Today's POD features another "unknown" something...unknown to me, at least.  Looks like there might be some sort of "step" or ledge in the background &, possibly, a pathway.  Would be nice to know where these pics were taken.

Jimbo   8-)