Unmarked Grave is a mythical location in Red Dead Redemption II.
In the middle of a forest, halfway from Van Horn to Annesburg, there is a strange grave, not marked on the game's map. It appears to be a buried corpse, marked with a stick crucifix. There's name "Bennet" engraved on the wood. It is most likely one of the 3 brothers that appear in the game's lore, but there may be also a connection with the Sawbone Clearing. It's a cabin near the grave that may look like it's abadoned, but there's a woman named Mrs. Londonderry that lives there with her son. The whole structure is mysterious, and it's been said that strange occurrences may take place during night time. It is not possible to enter the Sawbone Clearing cabin in free roam.
Creepy ambient music
In Red Dead Redemption II (and other newer Rockstar titles) there's a dynamic BGM system. Its purpose is to build up the right atmosphere in-game. Approaching the Sawbone Clearing or the Bennet's grave itself, causes the strange and creepy ambient to play during both, day and night. The place around the gravestone is especially spooky during the foggy weather. These conditions also often cause players to mistakely notice human like figures and scary shapes, that are in fact just bushes and small trees. It has also been said, that if the player is riding on a horse around that area during the night, it may get nervous.