This Welcome to The Hidden Side (70427) ghost-hunting toy combines the open creative play of LEGO building toys with an app – so interaction with the model triggers events in the digital world. Digitally interactive building toy for kids This Welcome to the Hidden Side model reveals a ghostly world when viewed through a smart device equipped with the free LEGO AR app. Kids then get to hunt ghosts, battle the boss ghost Lady E and explore and solve mysteries, either alone or online with friends.