Measuring 1.5 hectares in area in the heart of Lisbon, Estufa Fria consists of three parts: the original Cold Greenhouse (Estufa Fria), Hot Greenhouse (Estufa Quente), and Sweet Greenhouse (Estufa Doce). The term "cold greenhouse" comes from the original building's lack of mechanical heating: wooden slats regulate sunlight and protect the plants from excessively hot or cold temperatures. 

The garden opened in 1933, built near an old basalt mine which had been abandoned after a spring was discovered nearby, Portuguese architect Raul Carapinha conceived and designed the project. In 1975 the Estufa Quente and Estufa Doce sections opened, expanding the botanical collection to include plants from tropical and equatorial regions.

Source: Wikipedia