Still more scary mysteries for sleep-overs / Lists

Just some books that caught my interest and make me want to read

Looking for a scary story I read as a child. A young girl finds an old mail sack out in her garage or equivalent. There is a letter inside the sad. She reads the letter, aged and parts of it blurred, and finds out some booty or treasure has been hidden behind the fireplace at a house in the same town. She goes there and it’s super abandoned. She pokes around the fireplace and discovers a hidden cavity, which she crawls into. The door somehow locks behind her and traps her in the small space. She can feel scratch marks scratched deeply in the wall. She realizes the smudged letter said body, not booty. Then she hears some shuffling movement in the passage behind her.