For more "best" practices for megadungeon design, see my megadungeon design page.
Provide Non-Lethal Entrances & Exits
I was reminded of this from Paul's Blog and a lethal series of well-climbing trips into and out of Rappan Athuk.
Avoid having the main - or even only - way into a dungeon be potentially lethal. Even if you allow for precautions and care, if you can get wounded or killed getting into the dungeon on a bad roll you're discouraging delving.
Risky entrances are okay, but if the only way into and out of a dungeon is potentially lethal, you're actively discouraging players from exploring the dungeon. It does help explain why the dungeon isn't fully looted. But it also means players have incentives to:
- find another way in or out;
- find another dungeon;
- cut exploration short to maximize their chances of getting out of the potentially lethal entrance.
A lethal entrance pits the logic of the gameworld (dungeons should be hard to get into to explain why they have loot in them) vs. the logic of the game (players don't want their PCs to die and the GM wants them to enter the dungeon.)
Having a lethal or risky entrance that otherwise avoids other problems - it's unguarded, it's closer to deeper levels and more loot, it's more convenient, etc. - is a useful tool. But if it's the only way in and out, you're enforcing a tax in lost PCs to play the game. That's probably contrary to the goals of having a megadungeon in the first place.