About
The Wundersteine bricks are made of a shiny and hard plastic, with a glass-like sound when dropped. After several decades the bricks hold up well and are easy to build with.
It is unknown exactly when Wundersteine was first made, but sometime in the mid 1950's is likely, and not lasting long, maybe to the early 1960's.
The bricks come in a variety of shapes and types, closely resembling LEGO from the 1950's and their LEGO System / Town Plan era.
Here are some pictures:
The flat windows and doors
The flat windows and doors look very similar to LEGO, but there are enough differences to tell them apart. Starting with the door it does not have a door knob (small circle), and the windows/squares on the back of door are smaller. On top of that the door and windows are slightly less wide than LEGO. It is easy to see on the door, but on the windows it is mainly the "edges" which slide into the slots in the bricks that are thinner/shorter than LEGO.
You can also find some more pictures and information about Wundersteine here: https://www.inverso.pt/