Eighteen-year-old Lilja (Ilmur María Arnarsdóttir in an enthralling debut) visits her estranged grandparents Áróra and Grímur, in the city as she undertakes auditions for an international art performance group. Her grandparents welcome her, delighted with the opportunity to get to know their granddaughter better. However, when her father, Magnús and his younger sister Vala (Stefanía Berndsen, A WHITE, WHITE DAY) , two of Áróra's and Grimur's four children, find out about Lilja’s stay in the family house, a sense of panic arises. The eerie house has an air of mystery and as she stays there, Lilja begins to observe her grandmother's peculiar behaviours. When the family gathers in the home to celebrate Lilja’s acceptance into the art group, a dark secret emerges. Soon a seemingly normal family celebration turns into a horrifying tragedy that nobody could have foreseen. With mounting foreboding and recurring themes of water, writer-director Helena Stefánsdóttir’s debut film NATATORIUM is a claustrophobic, ominous, slow-burn drama centred on family dysfunction and secrets.