Shortly after Russia invaded Ukraine last year, Christine McGuire’s museum began receiving inquiries unlike anything she’d previously encountered during her career.

“We had people asking us if we still functioned as a fallout shelter,” said Ms. McGuire, the executive director of Diefenbunker: Canada’s Cold War Museum. “That fear is still very real for people. It seems to have come back into the public psyche.”

The Diefenbunker still has most of the form and features of the nuclear fallout shelter it once was for Canadian government and military V.I.P.s. But the underground complex, decommissioned in 1994, has shifted from being a functioning military asset to being a potent symbol of a return to an age when the world’s destruction again seems a real possibility with a nuclear-armed Russia raising the specter of using the weapons.

The Diefenbunker history is not just of global tension but also of Canada’s parsimonious approach to civil defense, optimistic thinking about the apocalypse and Canadians’ antipathy toward anything they perceive as a special deal for their political leaders. Now, the privately run museum is one of the few places in the world where visitors can tour a former Cold War bunker built to house a government under nuclear attack.

These factors have made the four-story-deep, 100,000-square-foot warren of about 350 rooms into an unexpectedly popular tourist attraction despite its off-the-beaten-path location, in the village of Carp within the city limits of Ottawa, Canada’s capital.

Robert Bothwell, a professor of history at the University of Toronto, was on the board of an Ontario cultural organization during the 1990s when a group of volunteers proposed turning the bunker into a museum. At that time, he said, several other volunteer-based museums had failed to attract visitors even with ample funding.

“So I thought: ‘Diefenbunker? Give me a break,’” he said. “But I was totally wrong.”

Since its construction began in 1959, the bunker has carried a variety of official names: Emergency Army Signals Establishment, Central Emergency Government Headquarters and Canadian Forces Station Carp. But it came to be known as the Diefenbunker after John Diefenbaker, the prime minister who commissioned it, more as a form of mockery than in his honor.