(I'm assuming you're talking about Might and Magic VI...)

I don't want to give it away, so for now I'll just say it's not in those two chests. There are another set of chests to find in a hidden room.

In other words, you don't find both the enemies list and the key at the same time. Those are two different quests, so it kind of makes sense they are in different locations.

Edit: If you look at the map carefully you might perceive something out of view. Sometimes. It helps to actually look around by turning side to side (when in the game, not the map). I think it's kind of a glitch from the seams in the walls that allows yet-to-be-seen passages to show up on the map sometimes, especially with secret doorways. In some places in the game arrows or magic can pass through the seams, such as locked doors.

Edit 2: On the other hand instead of thinking the seams as a game glitch, in an RPG sense perhaps the construction of the doors aren't perfect, or have worn away the material a bit. That could be a good reason for unseen passages to be noticed on the map, too. It's kind of like something in the back of my mind noticed a difference, and it showing up on the map helps reveal what was noticed.

Which game?

Good point. It sounded like Might and Magic VI to me, so that's how I responded.

Don't forget there is also damsel in distress from paladin's quest in this dungeon.

Silver Helms + Misty Island + Gharik's Key + Gharik's Forge = MM6.

Also, the key might not exist. I don't remember if the base GOG install uses the patch, but one patch removed the key and the lock on the Forge because of an issue with how maps respawned (Forge door would be relocked, but key wouldn't be respawned, which could prevent a player from finishing the game if they hadn't cleared the Forge yet).

Might want to try the Seer. Not likely if you didn't have the key. But maybe the Game reads it as "lost" rather than never found.

Patch didn't remove key and lock. It simply made it so once you open the door, it will be always open after respawn.

I stand corrected. I knew there was a fix for the forge, and my memory says the fix was just leaving the door unlocked completely.