I heard about this awhile ago and filed it under dumb facebook shit, but now my grandmother wants us all to read this book that "says some real interesting stuff about what shapes say about the world". Is there anything I should know about this particular type of nonsense?
The core of truth in sacred geometry is that there are shapes, patterns and proportions that you find across different cultures and in nature.
The explanation for that could be that God did it or that (white) aliens taught "primitive" humans about them. A much more likely explanation is that some patterns and symbols are simply easy to come up with because of their simplicity or that some shapes offer structural benefits. I.e. the reason why you have pyramids all over the world is that the pyramid shape is one of the easiest ways of putting rocks on top of eachother without the whole thing falling over.