PARIS (AFP) - It is one of the greatest and most visited art museums in the world, and the only one in an old railway station. Thirty years after the Musee d'Orsay opened its doors for the first time, it has become as much a Paris landmark as its big sister the Louvre just across the River Seine.
But the very success of the museum best known for its unrivalled collection of Impressionist paintings is now causing it problems.
An average of 3.5 million visitors a year pour through its spectacular vaulted nave, making it the "most dense museum in the world", according to its director of collections Xavier Rey.
There is simply not enough space, he said. Although the Musee d'Orsay is one of the top 10 most visited galleries in the world, it is several times smaller than its rivals.
"It will probably be difficult to welcome any more visitors," said Guy Cogeval, who heads the museum and its smaller offshoot the Orangerie, which houses Claude Monet's water lily murals.
Cogeval, who is stepping down in March, said the "one of the greatest challenges my successor faces is how to deal with this".
That lack of space will be severly tested this weekend when it opens its doors for free to celebrate its 30th birthday.
But the real problem isn't so much the public as finding a place to show its staggering collection of late 19th-century and early-20th century masterpieces which runs from Courbet's notorious "The Origin of the World" to Manet's reclining nude "Olympia" and Van Gogh's searing self-portraits.
While the museum is packed with some of Degas, Cezanne, Gauguin and Toulouse-Lautrec's best work, only around 4,400 pieces can be shown at any one time.
That leaves some 164,000 paintings and sculptures in its stores, which is set to grow even further with the massive donation by a Texan couple of their 350-million euro ($372-million) art collection to the French capital.
Businessman Spencer Hays and his wife Marlene last month signed off on the first instalment of 187 works for the Musee d'Orsay including pieces by Degas and Modigliani worth around 173 million euros.
Their gift, the biggest from a foreign benefactor to France since World War II, also includes important work by Bonnard, Vuillard and Redon.
Some 140 works by Bonnard and Vuillard were also given to the museum in January by the French collector Jean-Pierre Marcie-Riviere.
Faced with such pressure, the museum has bought a neighbouring 18th-century mansion on the banks of the Seine to house its library and research centre on the post-Impressionists.
The idea of a fine art museum in a railway station was revolutionary when the museum opened in December 1986. Not that the Art Deco terminus was your average transport hub.
Built like the Eiffel Tower and the Grand Palais for the Universal Exhibition in Paris in 1900, it had the same architectural exuberance.
Having survived demolition plans in the 1970s, it was converted into a museum for mostly French art dating from the revolutions of 1848 to the outbreak of World War I as one of the late French president Francois Mitterrand's "grands projets" to renew the French capital.
A runaway success from the start, with its architectural elegance and head-turning collection equally praised, Rey said that "one can no longer imagine the museum anywhere but in this station".
With another show featuring Van Gogh to open in March, it's biggest hit remains the exhibition questioning if the Dutch artist was really mad - "Van Gogh-Artaud, the Suicide of Society" - which brought in more than 654,000 people in 2014.
Some of its biggest successes have even surprised its curators, with almost half a million people flocking to see an exhibition this year on Rousseau, who was derided as a "Sunday painter" by his contemporaries.
A 2013 show on the male nude in art, "Masculin, Masculin", which Cogeval curated, was "to my great surprise a very big popular success with 430,000 visitors," he said.
The surprises don't end there.
The so-called academic painters from the mid-19th century, who had long fallen out of fashion like William Bouguereau and Charles Gleyre, are now having an unexpected resurgence in popularity, said Rey.