Thin strips of swamps typically won't have crypts but they are good to farm up other resources.

You want a larger and wider swamp. You typically won't see crypts from a boat unless they are really close to the water edge.

Most smaller swamps won't have any crypts. Some may have one, but I have seen larger swamps with over 20 crypts.

When you are out exploring, if you are worried about death and losing the key, I would suggest leaving the key at home and putting a portal on top of the crypt entrance when you find one. Makes it easier to jump back and repair as well.


They look like this, sorry it isn't a great shot. Kind of surprised I don't have a better one.
https://steamcommunity.com/sharedfiles/filedetails/?id=2587235525