I found this at an Op Shop a year or two ago for only $1. I used to love these toys. I had dozens of the larger size ones as well as the really big play set ones. I sold them all to my house cleaner for money to buy Star Wars toys instead. Pretty annoyed about that now because these toys were heaps of fun.
Each set is usually a head of a monster of some description which folds open with several tiny figures inside. The inside forms an interactive play set with various traps and other moving parts which were quite fun. This one in particular is only a small one so it is pretty dull but makes me nostalgia pretty hard.