Another lesson or two on megadungeons, based on my experience.
The rest of the series is linked from here.
This time out: hidden rooms.
The PCs in my game found a secret room, one with no door to discover until they'd located a lost (magical?) key. The found it with good mapping and by process of elimination - they determined there was no other way into this area, there was space for a room, and they had used magic to determine something (specifically gold) was there.
This isn't a new thing, as far as megadungeons go. But it did provoke some thoughts.
Use secret areas. Pretty simple - hidden areas are a reward for thoroughness, and are a good place to put "untouched" things in an otherwise well-traveled area.
Give multiple hint about secret areas. Unless you want to solely reward meticulous mapping and really good rolls to detect secret doors, or magical scanning, you need to allow a few ways to detect it. If the only way to find it is to stumble across it, or do something really non-obvious and bizarre ("You have to walk past it twice chanting while carrying the broken dagger hilt from room 17"), you're missing out on using secret rooms as a reward for effective play. Multiple clues can give a reason to check an area for a secret or missed area.
Here are some ways to do that (just a handful, this isn't exhaustive):
- allow magic to detect the rooms, or something in them (where it otherwise can't be, unless there is some room).
- it it's a puzzle entrance, allow multiple channels for hints on its solution to get to the PCs. Rumors, sages, hints in the dungeon, etc. That way a blown reaction roll from the one sage that knows or a single misinterpreted rumor won't mean your secret area remains forever secret.
- consider putting secret rooms in a pattern or a broken pattern ("these hallways have 3 rooms on the north side and four on the south. This one only has 2 rooms and a big stretch of blank wall. Let's check that.") This rewards comprehension of what is and what should be, not just thoroughness.
Corollary: You get the mapping behavior you ask for.
If you make tiny secret rooms that can only be reliably detected by meticulous mapping, with no 10' square misplaced on the players' map, you will get meticulous mapping. Sure, you can hurl wandering monsters at the PCs. But your careful secret room placement that demands careful mapping is a demand by you, the GM, that the PCs do this or miss stuff. So you end up in the odd position of punishing them for doing thing you demonstrated to them they need to do.
If you make bigger secret rooms that can be detected with a roughly accurate map, they are more likely to be found without long game session time spent on making sure their map exactly matches your map in all the particulars. If close enough is good enough, they'll settle for close enough. If perfect is necessary, they won't settle for less than perfect.