Fehn died in a retirement home in Oslo on Feb. 23, his grandson Jacob Fehn told the Associated Press.
Born in Kongsberg, on the outskirts of Oslo, in 1924, Fehn graduated from the Oslo School of Architecture and Design in 1949.
He received international acclaim in 1958 with his Norwegian Pavilion at the Brussels World Exhibition and again in 1962 with his Nordic Pavilion, built around live trees, at the Venice Biennale.
Describing building as an act of brutality, Fehn said he aimed to create harmony through his constructions.
"When I build on a site in nature that is totally unspoiled, it is a fight, an attack by our culture on nature," Fehn once said. "In this confrontation, I strive to make a building that will make people more aware of the beauty of the setting, and when looking at the building in the setting, a hope for a new consciousness to see the beauty there as well."
Most of Fehn's works are in Norway, including the white concrete Glacier Museum, which has been hailed as a landmark within contemporary architecture. Completed in 1991, it stands on a plain carved by Norway's Jostedal Glacier at Fjaerland Fjord.
He also built the Aukrust Museum in Alvdal and the Hedmark Cathedral Museum in Hamar, which has ramps and galleries overhanging archaeological ruins.
"Hedmark is my meeting with the past," Fehn told The Times in 1997. "To tell the story you have to manifest the present, so that there can be a dialogue between the two."
That year, Fehn was honored with one of his field's most prominent accolades, the Pritzker Prize, for his ability to give "great primacy in his designs to the relationship between the built and the natural environment."
As Fehn explained to The Times, "Architecture has to have a story to tell -- about people or architecture or nature. If you can establish a poetry about things, then you have a starting point."
He is survived by a son and four grandchildren.