Some films feel like blockbusters and some don't. Rachel McAdams thinks the upcoming Sherlock Holmes falls into the former category.

Set to open at Christmas, Sherlock Holmes stars McAdams as Irene Adler, the formidable foil and part-time lover of Holmes (Robert Downey Jr.). The role of Adler is expanded far, far beyond that of her print counterpart in Arthur Conan Doyle's original Holmes stories, as she figures prominently in only a few pages of a single story, "A Scandal in Bohemia," and is mentioned briefly in other stories, including "His Last Bow." McAdams' co-stars in the film include Jude Law as Watson and Mark Strong as Lord Blackwood.

"Oh yes, definitely, I think it is," McAdams replied when asked if she considered Sherlock Holmes the biggest potential blockbuster she's ever been a part of. She spoke in a group interview on Saturday in New York while promoting her latest film, The Time Traveler's Wife.

Working on the set of a film as massive as Sherlock Holmes "was so fun," she said. "It was so fun because everything is so realistic. We're shooting in the real dungeons of London, and I had the most beautiful costumes. Everything is fairly authentic. That was great."

McAdams smiled while describing the chemistry between Adler and Holmes. "We do have a certain kind of chemistry," she said coyly. "It's like an experiment gone wrong. We tangle in an interesting way." Sherlock Holmes opens Christmas Day.