Murder At The Gallop.

An adaptation of the Agatha Christie novel After The Funeral, Miss Marple ends up stumbling upon a mystery while out collecting for charity when she witnesses a man drop dead right in front of her. When she overhears the dead man's sister at the funeral remark that he was afraid that someone was trying to kill him and later discovers that same woman brutally murdered hours later, she decides to investigate when the entire family gathers again at the reading of the will.

The vast majority of the movie takes place at a hotel in the English countryside and in and around the hotel, where Miss Marple uses the public areas to eavesdrop and discover other such clues that would be useful to the investigation.

If you're willing to check out feature-length TV shows, then also check out ITV's Marple series which has some strong episodes set in hotels.

In The Body In The Library which was also the pilot, Miss Marple ends up getting involved in a murder case when a dead body is dumped in the library of her friend's country manor. Following some investigation to determine her identity, she learns that the victim was a dancing instructor at a seaside hotel, resulting in her staying there to investigate just how in the hell a complete stranger turns up dead several miles away.

In Bertram's Hotel, the entirety of the film takes place at a hotel. When Miss Marple checks into the hotel she becomes embroiled in the investigation when one maid is found murdered on the hotel's roof and another, who has heard of Miss Marple's reputation of helping others, implores her to help. A femme fatale, a nasty inheritance dispute, stolen artwork and a hidden Nazi also complicates things further.