After six years of work by a cast of thousands, the Bolshoi Theatre is just days away from reopening night. Fragile tapestries have been taken apart and rewoven thread by thread, barely visible veins have been gilded onto the leaves of plaster garlands, and bits of long-hidden Venetian marble have been uncovered and replicated.

As if commanded by a maestro’s baton, each stroke of the brush, tap of the hammer and flash of the needle soar together in a sensory rush of deep red velvet and gleaming gold. The Bolshoi could always be called beautiful. Now superlatives are needed.

“Look at the crystal chandelier,” said Mikhail Sidorov, gesturing toward a 21-foot-wide extravaganza of crystal and light as he led a tour of the theater. “It’s as big as a subway tunnel. There are 15,000 crystal pendants on it.”

One chandelier required 400 grams of gold. Another took five years to repair and polish, crystal by crystal. An artisan named Evgeny Vasiliev learned French so he could understand the design of the chandeliers in the White Hall upstairs. Then he made his own tools. Crystals had to refract light exactly as the originals. No effort was too big, no detail too small.

“The people who worked on this were mad — mad in a good way, of course,” said Sidorov, spokesman for Summa Capital, the construction company supervising the work. “They are extraordinary.”

The walls on the first floor still smell of fresh dusty-rose paint. When Sidorov leads a tour, his visitors must wear blue plastic booties. The floors will be pristine for the invitation-only-by-President Dmitry Medvedev concert Oct. 28.

The story of the Bolshoi is operatic in scope. Here it is known as the home of Moscow’s most famous ballet troupe and opera company, though occasionally it is used for galas and concerts. It was founded in 1776 and moved to its present site, just down the street from the Kremlin, in 1780. The building burned down in 1805 and was badly damaged by another fire in 1853. In World War II, it survived a bomb.

When the building was closed for repairs in 2005, the work was supposed to take three years. But the foundation turned out to be crumbling. “That was the most frightening moment for me,” said Anatoly Iksanov, the theater’s general director, “realizing this huge building was sinking on its foundation. This historic building was seriously threatened.”

In 2009, auditors said that contractors had misspent millions of dollars, and Summa Group, a large investment firm that has engineering and construction companies among its holdings, was brought in to take over. The cost of the renovation was reaching $660 million, 16 times the original estimate. Latest reports put it near $800 million.

More than 3,000 artists and engineers and laborers have worked on the repairs. Two years ago, after the foundation was made solid, interior renovations began, and they continue 24 hours a day, Sidorov said.

The acoustics presented a major challenge. During the Soviet era, concrete had been poured in place of elm in the orchestra pit, ruining the sound. Where papier-mache was needed, plaster was used. “It took us several years,” Sidorov said. “Look at these panels — they are resonant and we needed to test every one of them, and there are more than a thousand of them.”

The chairs in the orchestra section, designed for hardened Soviet bodies, are covered in red velvet and have been made larger, to accommodate today’s more upholstered theatergoer. There’s an area for the disabled (“invalids,” as Russians say) and another rarity in Russia, toilets for the disabled.

The stage, now movable, can be adapted for opera or ballet, and dancers should have softer landings with a special floor covering.

A second-floor hall, sometimes used for rehearsals, had been painted white in the Soviet era when it was used for Communist Party meetings. Artisans re-created the lovely trompe l’oeil of the original. In the czar’s foyer, wool and silk tapestries damaged by an unfortunate attempt at dry cleaning in 1974 were repaired. Other wall coverings were rewoven.

Rehearsal areas are spacious, and performers have been provided with more than one toilet and shower per floor. “The artists are very happy,” Iksanov said.

In the back of the main hall, two telamones hold up the czar’s box, now crowned with the double-headed eagle instead of the hammer and sickle. The telamones, statues of bearded men, their bare chests girdled in gold, bend their heads under the weight on their shoulders, as they have for nearly 150 years. Three tiers up, two golden children carry a lighter load. They look toward the stage, as if ready for the curtain to rise on the next act in the Bolshoi’s long career.