Walter Burns (Cary Grant) is a hard-boiled editor for The Morning Post who learns his ex-wife and former star reporter, Hildegard "Hildy" Johnson (Rosalind Russell), is about to marry bland insurance man Bruce Baldwin (Ralph Bellamy) and settle down to a quiet life as a wife and mother in Albany, New York. Walter determines to sabotage these plans, enticing the reluctant Hildy to cover one last story, the upcoming execution of convicted murderer Earl Williams (John Qualen).
Walter does everything he can to keep Hildy from leaving, including setting Bruce up so he gets arrested over and over again on trumped-up charges. He even kidnaps Hildy's stern mother-in-law-to-be (Alma Kruger). When Williams escapes from the bumbling sheriff (Gene Lockhart) and practically falls into Hildy's lap, the lure of a big scoop proves too much for her. She is so consumed with writing the story that she hardly notices as Bruce realizes his cause is hopeless and returns to Albany.
The crooked mayor (Clarence Kolb) and sheriff need the publicity from the execution to keep their jobs in an upcoming election, so when a messenger (Billy Gilbert) brings them a reprieve from the governor, they try to bribe the man to go away and return later, when it will be too late. Walter and Hildy find out in time to save Walter from being arrested for kidnapping.
Afterward, Walter offers to remarry Hildy, promising to take her on the honeymoon they never had in Niagara Falls, but then Walter learns that there is a newsworthy strike in Albany, which is on the way to Niagara Falls by train.

Question: Where did Walter promise to take Hildy for their honeymoon? 
Answer: Niagara Falls
Alternative answer: Niagara Falls.