Fallout 4: The Secret Room

Maybe a little bigger than a room, but the secret courtyard doesn't really have the same ring to it.

This can only be accomplished in the PC version of the game, and the code for it is "coc qasmoke" without the quotation marks. In it you will find every item in the game, whether it is a miscellaneous tea cup or a nuke launcher; it will be there. You will also find every crafting table as well as a variety of different power armors.

In Skyrim the selection was way more vast because they added every single enchantment possible for every single possible weapon type. So the number of weapons you could find in Skyrim were something closer to maybe hundreds because of that. I also don't think you could find all the uniques; i would have to look at it again to see.