Your structures are just like the [Yonaguni monument](https://en.wikipedia.org/wiki/Yonaguni_Monument).

[![Yonaguni][1]][1]

They look like they are the work of supernatural architects, but after a couple seconds judging their artwork, they start resembling the work of an intensely stoned supernatural architect who just learned what geometry is. A little investigation later and you find out such structures exist due to natural causes.

In Yonaguni's case it was seismic activity underwater and it probably took millenia. In your case, you may have fungi that grow some tissues which are as hard as wood ([those were a thing before animals conquered land](https://worldbuilding.stackexchange.com/q/106278/21222)), or even concrete. Fungi are also a good candidate for the source of such structures because some tripping is involved. Here is [a timelapse video of some fungi growing](https://www.youtube.com/watch?v=b-nJ0ROGD14) - notice the geometrical patterns that some mushrooms are able to create, when their caps cast a net around them.

It just so happens that on your world, fungi grow absurdly fast - faster than bamboo grows in our world - and then, due to some chemical trigger, they consume their own [chitin](https://en.wikipedia.org/wiki/Chitin) and become a large heap of something that looks like dandruff (if you ever had a micosis and you treated it with ketoconazole, you know what it looks like), or dust or something else.

As to why the shapes of houses, stairs etc. - that attracts curious creatures, and the fungus may then feed on the litter those creatures leave behind. We know that if some stairs showed up in the middle of the woods and leading to nowhere in our own world, it would become a place of religious pilgrimage and some tourists would leave trash in the areas around it. It just so happens that your fungus can imitate a house to a very high degree of precision. It may release spores in the air that cause people to trip so as to complete the illusion - in other words, the paintings in those magic suburb homes are not actual paintings, they are just a plain, square piece of the fruiting body.

  [1]: https://i.sstatic.net/ChKrm.jpg