I see a key in there but can not get in
What am I missing?
Asking for a clue or help please

Spoiler alert:

I THINK I know where you're talking about (somewhere near the first couple of levels). It's actually real simple.
It's a bit of a lie when they say it's a no weapon area. All you need is to temporarily give up one weapon.
That enough? Good luck.

Yeah, simply place any spare weapon (I used a dagger) in the alcove opposite the door, and it will open. You can retrieve the weapon on your way out, if you have no spares.