- Country: Sweden
- Genres: Family
- Release: 1991-02-22
- Director: Clas Lindberg
- Writers: Clas Lindberg
- Language: Swedish
- Stars: Ulf Eklund , Gösta Ekman , Anna-Yrsa Falenius , Jenny Fogelquist , Gunnel Fred , Robert Gustafsson , Weiron Holmberg , Oliver Loftéen , Olof Rhodin , Kristina Törnqvist
- Runtime: 81 min
- Awards: 2 wins & 2 nominations
- AKA: Onderaards geheim (Netherlands the) , Underjordens hemlighet , Subterranian Secrets , Underjordens hemlighet (Sweden) , Unterirdische Heimlichkeiten (Germany) , Hemmeligheden under jorden (Denmark) , Ihmemaan salaisuudet (Finland) , Underground Secrets , Unterirdisches Geheimnis (Germany) , Sairaalan salaisuus (Finland)
- Plot: Nisse is hospitalized with severe asthma. He meets the seriously ill boy Lelle. Lelle is depressed and abandoned. He has a dream; to build a large airship and provide food for starving children in other countries.
- IMDB:tt0103163
Underground Secrets Cast · · · ALL
Clas Lindberg
Director
Max Vitali
Lelle
Oliver Loftéen
Nisse
Gösta Ekman
Carson
Kristina Törnqvist
Nurse Sara
Gunnel Fred
Nisse's mother
Hans Wigren
Nisse's father
Ulf Eklund
Doctor
Anna-Yrsa Falenius
Nurse
Weiron Holmberg
Janitor
Robert Gustafsson
Young Man
Bojan Westin
testing nurse
Olof Rhodin
Robinson