Nightmare (Finnish: Nightmare – painajainen merellä; literally translated "A Nightmare on the Sea") is a 2012 Finnish horror thriller film directed by Marko Äijö. The film is based on Finnish soap opera television series Salatut elämät; one of the characters of the series, Peppi, is going on a cruise with friends, which is about to take a horrible turn.

The main partner of the film production was the Russian St. Peter Line shipping company, on which the filming was done on the Princess Maria cruise ship. The film's production budget was about €500,000, of which the Finnish Film Foundation's share was €200,000. The theme song of the film is the song "Kyynel kuuluu mereen" ("A Tear Belongs to the Sea") by the duo Vague Musik, with Karoliina Kallio as the singer.

The film grossed about €1.1 million, and it was awarded at the 2013 Jussi Awards with an honorary certificate as the audience's favorite. However, the film received a hostile reception from critics. Critics have given it mostly one star, and it has been described as "absurdly bad".

In 2014, the film received a sequel, Nightmare 2: The Nightmare Continues.