What is the glass castle? And how is it realistic or not

The glass castle represents father's delusional dreams that he presented to his children. The castle itself would be a magnificent transparent palace built in the desert and relying on solar panels for electricity. Of course, this castle would remain imaginary, just a symbol of the many empty promises father gave to his children.

When Dad wasn’t telling us about all the amazing things he had already done, he was telling us about the wondrous things he was going to do. Like build the Glass Castle. All of Dad’s engineering skills and mathematical genius were coming together in one special project: a great big house he was going to build for us in the desert.