A Lake Tahoe resort once owned by Frank Sinatra and frequented by his Rat Pack buddies is about to undergo a major makeover.

The Cal Neva hotel-casino that straddles the California-Nevada line has closed for more than a year to allow for the multimillion-dollar project.

The 219-room, 10-story hotel and 6,000-square-foot casino will be upgraded in an effort to revive the struggling property, said Robert Radovan, co-owner of Criswell-Radovan. His Napa Valley, Calif.-based development company acquired the Cal Neva in April.

“Our goal is to bring it back to its former glory and to make it what it was like in Sinatra’s day,” Radovan said. “It has such great soul and character, and it’s needed this redo for many decades.”

The property has fallen on hard times because of the recession and competition from Las Vegas and Indian casinos. Its casino shut down in 2010 due to declining business.

During its heyday from 1960 to 1963, the Cal Neva was owned by Sinatra and became one of the most famous resorts in the country. It drew fellow Rat Packers Dean Martin, Sammy Davis Jr. and Peter Lawford, and stars such as Marilyn Monroe, Joe DiMaggio and Juliet Prowse.

Monroe spent her final weekend at the Cal Neva before she died of a drug overdose in Los Angeles in August 1962. Five small cabins, including the one where she stayed that year, also will be renovated, Radovan said.

Sinatra renovated the Cal Neva, adding the celebrity showroom and a helicopter pad on the roof. He used tunnels to shuffle mobsters and celebrities beneath the resort so they wouldn’t be seen by the public. The tunnels were built in the late 1920s so liquor could be smuggled in during Prohibition.

The showroom will be improved with modern equipment, painting and new carpets, Radovan said, and the tunnels will be preserved. Tours of the cabins and tunnels will resume after the project is completed. Bigger plans are in store for the showroom. “The acoustics in that place are amazing. The modernized equipment will allow for high-end concerts,” Radovan said, adding the room where Sinatra, Martin and Davis once performed will continue to be named after Sinatra.

Owners hope to make the hotel a 4-plus-star resort instead of a 1-star by upgrading rooms with modern amenities, larger bathrooms and bigger windows offering Lake Tahoe views, he said. Plans call for the redesigned casino to reopen with blackjack and other table games.

Owners hope to reopen the Cal Neva on Dec. 12, 2014, which would have been Sinatra’s 99th birthday. He died in 1999.