“There no be anything here . . . Maybe wizard have something down well and use rope? . . . Maybe trail go up and use rope to up more . . . Maybe potion go boom and make wizard bearowl all time?”
Jorund is very confused but seeing that the house is empty he puts away his hammers.
Okay… Read Magic shows up nothing on the book. It looks like a job for a skilled reader of English or else a Comprehend Languages. Many of the pages are partly burnt and some crumble as they are turned, but there are some that still look readable.
The grapnel rope could easily reach to the roof and down to the ground on the other side - it’s a good 50’ coil. However, you do notice that it’s quite damp, which may offer something of a clue.
Ulf feels the grapnel strike against something underwater, and after a few tries he manages to snag it, and draws up a smallish well-made iron box with a ring in the lid. The box is heavily greased.
Osvald peers at it from a distance, without touching it. Just to see how it opens and such- studying it. “Say Ulf… how heavy did the box feel coming up?”
Osvald notices the grease “Hmmm- that could be one of two reasons most likely- either its waterproofing the box… Or if we open it, there’s a good chance the box could go boom! And then the grease certainly would not be fun to deal with afterwards- what with the screaming and the burning. That could be done by magical means OR by an actual phsyical trap, since it’s coated in grease. Very clever indeed… Oooh, I wonder what’s inside!”
It appears to be untrapped and unmagical. As for the door key, that’s about a hand’s width too big. Note that the box is heavy, and if it owes any of that weight to a lead lining, Detect Magic might not read through it.