"RING RING"

A mockup of the old ABBA studio features a self-playing piano connected to Andersson's current music studio - each time the musician plays on it, the piano plays as well.

The museum walls are plastered with newspaper cuttings, fan mail and videos. Visitors can peer into a behind-the-scenes dressing room, admire ABBA's gold and platinum discs and see a reconstruction of the Swedish cabin where they composed songs.

Based on the band's first major hit "Ring Ring", the museum also includes a red telephone. Only the four band members have the number, and they promise occasionally to call it and speak to surprised visitors.

After ABBA, Ulvaeus went on to become a businessman and helped to produce the hugely successful "Mamma Mia!" musical that was later turned into a film. He has been the main ABBA member behind the museum.

ABBA became one of Sweden's biggest exports with hit songs like "Dancing Queen" and "Gimme! Gimme! Gimme! (A Man After Midnight)".

The group sold around 370 million records in total and are part of a rich Swedish pop tradition which includes Roxette, Ace of Base, Europe and Kent.

But the museum took a long time coming. Separate plans for an earlier ABBA museum were shelved in 2008.

Stockholm has been struck by a bout of ABBA fever in the buildup to the opening. Visitors to the international airport are greeted by life-size pictures of the group as well as dancing Spitting Image puppets.

Baggage belts have "Gimme Gimme Gimme" emblazoned on the sides.

"I walked with Frida yesterday around the museum and she had a tear in her eye," said museum director Ingmarie Halling, ABBA's former costumer and hair designer from 1977 to 1980.

"Here you follow the footpath of ABBA. But you have to walk gently when you tell someone else's story."