Went to a camping in the Laurentians in Québec (Ste-Agathe) and there were those things near some camp sites. The sites are only accessible by footpaths. No car access. And if you bring a bike, you have to walk it up a hill, so I doubt they are bike racks.
EDIT: I have sent an email to the park and they have been kind enough to reply. It's just a type of fireplace with a grate. They didn't give more info than just this. Thanks to everyone for pitching in!
Here are a few more pictures for context
And I don't know about the past of the site. It's a municipal camping close to a lake and hiking trails. It may have been open during winter in the past but I doubt it because campings here are all closed by the end of November. However it can still be part of a network of ski trails, and be places to take a break.
Also, gathering wood for fires is usually forbidden on such sites and you have to buy a bag/bundle at the reception.
I gave it a try here hoping maybe someone would know exactly what these are, and so far everyone has good guesses, but it's still guesses.