The power level of my megadungeon has changed over time.
The Original Power Level
From the start, my megadungeon was aimed a bit higher than a starting power level. For one thing, the original concept of my game was just play some DF, and it was only after the process started to get rolling that I decided I wanted to try my first-ever megadungeon. So naturally, I had the opportunity to build a dungeon that wasn't just rats and goblins on level one, aimed at hapless starting would-be heroes.
I put in some tough fights right away, and made sure there were legitimate reasons why lesser adventurers hadn't plundered the hell out of it. Basically, I used a mix of:
- difficult entry points
- a ghost-haunted ruins
- a murderous stalker that emerged from the dungeons to hunt
- lethal monsters near the entrances
- rumors that it was a dry hole, treasure wise
The idea was to explain why others hadn't been trucking in and out.
Some of the things I added were straight-up homages. There is a pool room on level one full of magical pools (a B1 reference). There were trolls, because I'd heard it said that Greyhawk had a nest of trolls on level one (plus, I love trolls and I own a bunch of troll minis). There was an evil temple with smoky demons waiting to kill all who entered (a "Treasure of Tranicos" Howard/de Camp reference*).
But other stuff was there directly to challenge experienced DF guys, and GURPS Dungeon Fantasy guys start out quite powerful compared to normal adventurers, nevermind the usual types you'd get in old-style D&D games. Gargoyles immune to most of the attacks of normal adventurers. Unavoidable traps. Lethal double encounters. A mass of wights, capable of committing a casual total party kill. Hobgoblins in pillboxes accessible only from the level below using poisoned arrows and harassing fire. Stuff of that sort.
In other words, the dungeon's power level even on level 1 was enough that it took fairly tough adventurers some effort to crack the level and move on further in the dungeon.
It didn't stay that way, though.
The second stage was of diminished power. The trolls were killed. The gargoyles subdued. The wights destroyed. And so on. Even the barriers to entry had been dealt with. By a dozen sessions in, most of the issues that would keep people out were gone, and treasure started to flow from the hidden spots in the dungeon.
For a while, the upper levels were freely accessible to the party, and even a lesser group of adventurers could mess around there without big problems (albeit, without big payoffs, too).
So the next part was a dip in power.
Again, this didn't last.
Barriers to Entry
The current state of the dungeon is one of much danger. Even though the party has killed a plethora of monsters, more have appeared. Some things from below have moved up. Some things from outside have moved in.
Not only that, but a plan by the players to keep out interlopers (NPC ones) has clearly backfired. They armed, paid, and encouraged some orcs they encountered to expand their control and hunt their enemies. To a degree, this has worked (the cultists they wanted dealt with haven't made an appearance since) but it has also meant the dungeon is less accessible.
The formally chaotically occupied upper levels became sparsely occupied and mostly looted, and now to occupied and patrolled by orcs (at least, the areas the PCs can access.) A dragon was slain for access to the lower reaches, but even as the PCs smooth out their own path into the depths of the dungeon the orcs have attempted to follow. It's gone from raiding a set of tunnels full of monsters for their stuff into that plus evading and outsmarting an intelligent body of foes.
As such, entry into the dungeon by a beginning group of adventurers is pretty much impossible. You'd need a substantial force to get past the fortified orc-held entry points, and the other entry points are known to the orcs (and thus untrustworthy), or known to the orcs but lead straight into very dangerous areas.
So oddly, even as major groups of foes have been wiped out, monsters slain, and traps dealt with, Felltower has steadily gotten more dangerous to less experienced adventurers.
In other words, level one has gotten more dangerous the more play has gone on, not that play in the dungeon has moved to deeper or more lethal levels and left an empty level one behind.
Interesting - it's not what I would have expected.
* Yes, I know the original story is "The Black Stranger." I know even the idea of reading the de Camp revisions makes some people so angry they'll foam at the mouth. But TBS doesn't have the exact bit I thought was so cool and lifted, and ToT does.