TORONTO -- Filming parts of the gripping wartime drama "The Imitation Game" at the British estate where some of the biggest secrets of the Second World War were cracked wide open was a somewhat "ghostly" experience for stars of the film.

At the same time, shooting scenes at Bletchley Park -- once a top secret locale, now a tourist attraction -- was an honour, the cast agreed.

"It was wonderful to be on the grounds where these people lived and breathed and worked, and went about their day doing this extraordinary quiet, heroic, stoical work," said Benedict Cumberbatch, who plays Alan Turing, a brilliant British mathematician whose code-cracking skills help hasten the end of the Second World War.

"There's always a slightly surreal aspect to being somewhere where that character was, or using something that belonged to that character or anything that makes you sort of play with ghosts of the reality of it."

Keira Knightley -- who plays Turing's colleague Joan Clarke -- called filming at Bletchley Park an "amazing" experience.

"It's very moving actually," she said during an interview at the Toronto International Film Festival, where the film is playing. "It's a totally fascinating place, I really loved it."

There was a surreal aspect to the entire process though.

"If you do any film and you actually go to the actual places, and particularly when it has been kept like that has, it's absolutely been sort of preserved," said Knightley. "You very much feel that kind of locked-in-time. There is always something quite ghostly about it."

Ghostly "in the nicest possible sense" though, said Matthew Goode, who plays another Turing co-worker.

"One of the places that I liked, strangely, was a bar," Goode said with a cheeky smile. "That's where they went, when the whistle went at midnight and another day is done ... you kind of got the feeling that there might be some DNA of Turing lying around."

The whole experience helped bring depth to the performances, said Goode.

"It felt like it added a lot and we felt honoured to be there, because it was like this is the hidden story," he said. "This is where the heroes who still won't talk about what happened, who were normal people, lived. It was a real honour."

The Toronto International Film Festival runs until Sunday.