A poster at RPGNet asked for ways to describe certain types of challenges in-setting, rather than with just game statistics. Since all this was for a D&D(-like) game, the discussion was mostly for concrete descriptions of dungeon obstacles. I contributed these ideas:

Door materials

1. Glass
2. Wooden, flimsy – a door whose strength is compromised due to thinness, poor construction, weak materials, existing damage, etc.
3. Wooden, sturdy
4. Wooden, reinforced – a door of superior strength owing to some factor like some slightly exceptional wood, excessive thickness, metal banding, or the like
5. Stone (you can probably apply the flimsy/sturdy/reinforced modifiers here under some circumstances)
6. Concrete (useful in Roman-like settings, where stone is desired but too expensive given demand)
7. Bronze
8. Iron
9. Mithril
10. Diamond
11. Adamantine (you may want to swap these last two)

As a general note I’d assume most doors in day-to-day life are wooden, with the door being sturdy if it’s intended to secure rather than merely partition one area from another and if material circumstances permit it (for example, exterior doors of dwellings would ideally be sturdy, but in the slums things may be run-down or otherwise of low enough quality to be considered flimsy).

On the Diamond/Adamantine order – I think D&D would like to hold adamantine as being at least a peer to diamond, if not its superior. Personally I prefer a sort of medieval way of thinking about it, where diamond is sort of like “true gold” (which was supposedly transparent and lined the streets of Heaven IIRC), or the noblest alchemical material, or something like that. Well, and I’m also nostalgic for the materials in Bard’s Tale, where the progression went MTHR -> ADMT -> DMND.

Lock types

I spent a while reading up on these via Wikipedia and some short histories of locksmithing, and one of the first things that was brought up is that locks mostly serve to buy time; a lock may be difficult to bypass surreptitiously, but if you don’t have to worry about the disturbance you create brute force can defeats all sorts of clever lock design (by e.g. drilling out the lock). So these entries are in order of increasing difficulty of surreptitious entry – blocking forced entry is a matter of special material, traps, or other circumstances.

1. Warded lock (can be bypassed by a skeleton key – this is basically the type of lock that anybody with proper equipment and basic training should be able to bypass by Taking 10). This would be the Rusty or Worn Lock category suggested by Frecus
2. Pin tumbler lock (the usual type of lock that everyone thinks of picking; Frecus’s Simple Lock)
3. Disc tumbler lock (can’t be bumped, so much harder to pick than pin tumbler locks. Intricate Lock)
4. Double acting tumbler lock (series of internal levers – the tumblers – falls into a slot on the bolt; bolt yields only if each of the tumblers is raised to the correct height, neither too low nor too high). Masterwork lock?
5. Detector lock – designed to detect attempts to open it with incorrect keys or by lockpicking attempts and to take a specific action (this could be used to trigger various traps – comes from the Chubb detector lock, which historically was a Masterwork lock or beyond (it took over 3 decades for the first successful picking attempt; many other locksmiths were unable to do so); its “false key” action was to jam in a locked position until a special key was used to undo the jam.
6. Bramah’s Safety Lock – I’d have to read about the mechanism more in order to describe it (see http://www.lockpicking101.com/viewtopic.php?f=9&t=47793), but among other things it removes feedback from individual pins. Over half a century passed before first successful picking attempt, despite a large prize offering; the attempt took 51 hours over 16 days; this would make it even further beyond a Masterwork lock than the Detector lock. Edit: the specific instance of Bramah’s Safety Lock that took all this time to pick was the Challenge Lock; if you want a more generic name (one that doesn’t involve a proper noun) you might use that.

That’s as close as I can find to a progression of lock-picking difficulty. You can create variations by coming up with complicating factors, e.g.

• Time-lock clock: (http://en.wikipedia.org/wiki/Time_lock) – some measurement of time – or perhaps another external condition – is taken, and the lock can only be operated when the condition is met. This is a good place to put magic in a lock, since the magic just detects a condition; simply nullifying the magic means the condition isn’t detected and the lock remains inoperable.
• Biometric lock (measures some biological qualities/quantities of the person opening it – perhaps the hand is used as a key, with certain finger lengths being used to lift pins; one might imagine a lock that assumes polydactyly, perhaps one for members of the royal family)
• Magnetic-coded lock – in addition to mechanically-operated pins, there are permanent magnetic pins matched to magnetic bits in the key. These bits drive the pins purely magnetically – they’re mechanically isolated. (http://en.wikipedia.org/wiki/Magnetic-coded_lock). Note that keys for this sort of lock can’t be reproduced by taking an impression or otherwise by sight (unless you can see magnetic fields)
• Combination lock (no exposed keyway = no lock picking per se, though these are by no means proof against surreptitious entry)
• Multiple locks – specifically, a set of 2 or more locks where the key has to be operated simultaneously (as seen in Wargames, for example). Quite difficult for a human to pick if the locks are far enough apart or if there are more than 2 of them.