Four years and almost five million euros later, Leonardo da Vinci's Mona Lisa has moved into spacious new digs at the Louvre Museum in Paris but her famous smile remains as enigmatic as ever.

Visitors will find the 500-year-old painting in the Salle des Etats, a large gallery that served as a parliamentary debating chamber until 1870 and which has undergone a €4.8 million makeover since 2001.

Peruvian architect Lorenzo Piqueras said he wanted to make it easier for six million annual visitors to find what is arguably the world's most celebrated smile, and to prevent the huge jams which used to built up in front of the masterpiece.

"I imagined someone coming to see the Mona Lisa, who was being told: 'Walk over there, turn right, turn left, there she is.' That's impossible," Mr Piqueras said, referring to Mona Lisa's old home in the cramped Salle Rosa at the end of a gallery.

The Mona Lisa is now smiling from a large structure resembling a giant picture frame right at one end of an 840-square-metre room, where visitors can admire her from behind a wooden railing. New lighting underlines the painting's colours.

"Here, you will walk right into her," Mr Piqueras said, pointing to the big entrance of the light room. "You notice her immediately, you walk towards her and see her all the time. I count on that to have fluidity in the stream of visitors."

The masterpiece, set against a marbled beige wall and protected by unbreakable glass, is displayed together with some 50 other 16th century Italian paintings, including the giant Wedding Feast at Cana by Veronese, right opposite her.

Louvre officials said last year the Mona Lisa showed signs of wear and have ordered an in-depth technical and scientific analysis to determine the painting's state.