|Trigger: Mechanical: Interaction||Effects:Onset Delay|
|Save: Varies||Duration: Instant|
|Resets: Varies||Bypass: None (Avoid)|
Description: Your players should really really know better. Somewhere in the dungeon they find a feature, such as a toilet, campsite, suspension bridge or other useful functional area or feature. Only the area is really a trap. The fire burns away until it explodes or perhaps there are well placed bolts to strike at a very uncomfortable place when the toilet seat is used.
Detection/Disarming: First of all, you should be aware that if you've been running a game for several weeks and the players run across something like this, nothing short of a million gold coins will cause them to fall for this trap. So it is important that you provide many areas like this and make them mostly harmless. Perhaps provide a temporary benefit either in mobility (Can carry more weight, is refreshed) or a small bonus to abilities (+1 to saving throws for 6 turns). You can even sometimes provide a large bonus for erratic reinforcement.
The idea is to train the party so that they look forward to these little amenities. Then when your delvers encounter one, they will not do the very simple and very basic detective work necessary to notice and disarm traps.
Most of the relevant agency for these has been covered in other articles ("Why yes, there does appear to be an extra hole in the toilet. Why yes when you examine it you discover that it does indeed contain a rusted iron bolt!") The key with a trap like this is training your players and using the idea of trap escalation to stymie their greedy attempts to empty out your Mega-Dungeon.