Here's a photo of the crypt in New Orleans Square. Dated 1764, it was supposedly to be part of the cross-theming for Frontierland (Tom Sawyer's Island) & New Orleans Square (The Haunted Mansion).
we've heard a few different stories, like tying Jean Lafitte to both the Haunted Mansion & Pirates of the Caribbean. Or that the crypt actually belongs to the pirate who built the Haunted Mansion. we've also heard that there was supposed to be a tunnel to Tom Sawyer's Island, and this crypt was part of that theming. There's another story, that the date 1764 is supposed to honor an Imagineer who did a lot of the work in New Orleans Square.
after doing a little bit of reading and research, we're not quite sure which is true.
anyways, we know that there are tons of secrets and hidden details like this at Disneyland. and we're looking forward to learning about more of them!