Repairing the High Labyrinth of Argent requires several hours of work. The chamber is an ideal place to bar the doors, rest, and recover spells, though. It's located on one of the higher (that is, nearer to the surface) levels of the dungeon, so that the players can and probably will come back to the chamber, but it represents some sacrifice of progress. This should be tuned to feel like a tradeoff, but a valid one.
Any number of different skills might work for the repair; if one were using D&D Next's skill list, I might suggest Athletics (handling the weight of the tiles without causing further damage), History and Religion (recalling the lore of how the High Labyrinth was structured), and proficiency with Artisan's Tools. For Quintessence of Dust, I might use Craft (Stoneworking), Insight (Gnosis), and Reason (Deduce, Engineering, or Solve Puzzles).
When reconstructed, a character can walk the labyrinth (ahem, labyrinths are not puzzles
- if I meant maze, I would have said maze). The character makes a difficult Wisdom or Insight check and spends an hour. On failure, the character gains a bonus to her next Insight check (that cannot be applied to further labyrinth checks). On a success, the character gains a bonus to her next Wisdom check of any kind. These two outcomes do not stack; the success result overwrites the failure result.
It's probably also a good idea to give the High Labyrinth of Argent additional exit paths, either to dungeon levels above and below, or directly to the surface. What with being
a labyrinth, I'd suggest that characters could make an alternate skill check in walking the labyrinth that teleports them to a surface location. That surface location might have a parallel teleportation into the dungeon - one particularly interesting version is a location that teleports characters into the High Labyrinth of Argent as their initial entry into the dungeon, only to reveal that there is no exit until they repair the mosaic or find a new way out. (Maybe they even have to track down unbroken tiles from other half-ruined mosaics in the dungeon.)
The Forge of Tsaritsa Aveline
Some years ago, the Empire of Koskjova suffered grave losses in war as a result of internal division and enemies on every front. As a result, it was necessary to rebuild the army as quickly as possible; thanks to a limited number of available soldiers, the defenders of the empire needed to account for thrice their number in battle, time and again. To achieve this, the Tsaritsa
Aveline ordered the construction of an innovative new design of blast furnace that made not steel but the true adamant, in the city of Oplot (= fortress) Drezna. It was a mighty citadel, responsible for defending the Empire from many of the dread foes that threatened it. Though they endured for many years and broke the great siege, the Empire's doom could not be stopped by any mortal craft.
With the fall of the city of Oplot Drezna, the Forge was ruined, but it could be restored by one with sufficient skill and dedication. The forge itself is in a massive chamber deep below the surface. Restoring the forge requires skill checks in the general theme of Artisan's Tools or Crafts, Thieves' Tools or Disable Security (to clear away delicate machinery without doing further damage), and Perception. This involves accessing several different areas - the air intake and vent are blocked near the surface, the chain of the trip hammer needs to be reattached in the mid-depths, and so on.
Once repaired, the forge can smelt adamant, repair damaged gear (if that's a thing in your system of choice, or if the party discovers damaged gear), turn relatively worthless raw materials found elsewhere in the dungeon into ingots of refined metals, and allow rapid ascent or descent between dungeon levels (by attaching oneself to the trip hammer chains). Finally, some part of the forge - the fire, the trip hammer, I dunno - is necessary to pierce a boss monster's nigh-invulnerability, so the PCs have to lure that opponent into the main chamber of the Forge and seal the doors against escape. (The point of this aspect is to ensure that there are at least two encounters here - one using the terrain powers of the forge in ruin, and one after its repair.)
Other Ideas That I'm Not Developing Right Now
I'm not writing up adaptations of the Waypoints that Below
uses, because I don't want to just lift +Chris Gardiner
's ideas. The general theme, though, is that when fully improved, each Waypoints purges two of the game's negative conditions, grant a small-but-useful amount of Gear, Secrets, or Treasure (the game's three primary currencies), and allow you to change your Depth. D&D doesn't handle negative conditions the same way that Below
do, but 3.x D&D has reasonably good parallels, while 4e has its disease track, and could probably stand to add a few more lasting conditions.
For more variety, I might add buffs of some kind - the Concentration rules of D&D Next would make this especially potent, if the location "carried" the Concentration requirement of the spell for a span of time. The problem then becomes setting things up so that players don't return to the location and renew buffs every single time the buffs expire. I imagine some kind of doom track timer in the dungeon, a scaling cost associated with the buff, or relatively heavy use of wandering monsters as all being workable.
The important thing is to make this
dungeon stand out from all of the other dungeons your players have seen for years. (I am personally not a huge user of mega-dungeons, but it's clear from reading a lot of the gaming blogs that most mega-dungeons are both playing to a narrow range of experiences and struggling to break out of that mold.) So don't be afraid to let the upgraded location radically change one of the core assumptions - just like the portal gun makes Portal
not like every other shooter you've ever played, let the players get deeply attached to one or more locations, and let its rules make this campaign unlike any (system of choice) they've played before.
You might do that by changing up how spells refresh within this dungeon or how hit points are regained. Maybe players can drink from a blessed well all they want and always return to full health, but doing so builds up some other negative quality? Radically changing the playstyle of the cleric class could be neat. I'd generally say to avoid making things worse for the players on the whole - you want this to be memorable for positive
The comments field is, of course, open to more ideas.