I'm sorry to hear you weren't completely satisfied with your stay especially hearing you didn't feel safe. We are very sad to hear that.
Leaving your bags for a couple of hours would of course have been nice but unfortunately it just wasn't possible for us to offer you this help on this exact day. Anyway, I'm happy to hear it wasn't a deal breaker for you.
The building and the apartment is indeed very old, actually historical, some find things like that beautiful, some just find it old. Each to their own taste.
In regards to the key situation, I do think you are mixing up which keys we are talking about. The key you've lost is to the front door of the apartment which is a completely new key, in fact only a few months old. I think, if someone lost the key to your front door you would most probably also make it in to huge issue, we did, not only because you didn't feel the need to tell us that you've lost it but also due to the fact that this affects the safety feeling in our own home not only for us but also for future guests.
Nevertheless we regret you felt unnecessary stress before your 10 hour drive.
Also, just to clarify, the "old" key that you are talking about is for the bedroom and it's actually an antique key so it kind of makes sense that you've never seen a key as old as that.
Anyway, I hope we'll find a solution together with airbnb very soon in regards to covering the repair cost for the damages that were made to the flat during your stay.
Once again, we are sorry to hear you weren't satisfied with your stay but we thank you for choosing our apartment and wish you all the best.