Lego Captain America & Iron Man set (from 2012 New York Toy Fair) for $11,200 (around £8,485, AU$15,590). The rare Lego Magician and Zombie (from 2015 Manager Conference) for $11,150.

LEGO, the world's largest toy maker, is quietly building its reputation as a good investment as select unopened Lego sets have an average annual return of 11%. That's more than gold.