Anyone knows what puzzle is and how to open it?
It's a Dovetail Cube Puzzle
and a Google search will show you the solution and/or how to build one. But beware that there are actually two different versions (with two different solutions).
Spoiler alert, click at your own risk of spoiling the fun of discovering the solution by yourself:https://www.google.com/search?q=dovetai ... e&tbm=isch