Ikea Trofast / Flisat Activity Lid 

A fab Large Sensory tray which fits into the large trofast bins
(40x30 sized trofast tray)

It comes in two pieces, a 3mm backing piece with little windows cut out and then a hollow 6mm piece which you can then glue to the base if you wish (Any white craft glue works well) 

Pop lights underneath to shine through the windows and doorway for a spooky set up !