Normally museums exhibit only a small proportion of their collections, but the Boijmans Van Beuningen gallery in Rotterdam will this week become the first in the world to show off the lot.
Housed in a huge mirrored, bowl-shaped depot attached to the museum in the Dutch port city, its collection of 151,000 artworks by artists including Vincent van Gogh and Claude Monet will be accessible to visitors from Saturday.
"It is the only fully accessible depot, public depot that is open in the world," museum director Sjarel Ex told AFP as media toured the building on Tuesday ahead of the opening.
"What happens here is that you do not follow the script that was written by a curator... you see things by coincidence, and you feel that you are discovering things and that you connect things."
Normally, only some six to ten percent of collections at major museums around the world like the Boijmans Van Beuningen are on display, the rest kept in closed storage depots, said Ex.
That will now change for the Rotterdam institution -- and visitors will even able to watch works being restored.
"If you do not show the works, and people stop talking about and thinking about an art work, it is very likely that it sinks into oblivion -- out of sight out of heart," he said.
The warehouse was originally created to solve a very Dutch problem -- the likelihood of flooding in a low-lying country where a third of the land sits below sea level.
The old cellars below the museum were liable to let in water, making them unsuitable for storage.
"Every building is a moment in time, so this celebrates for sure the climate," said its architect, Winy Maas.
"Why? Because it's the raison d'être of this building -- the former archives were under water. It was flooding, so we have to bring it up."