For those who are looking for ideas for challenging and unique encounters, here is a template for others to share ideas:

Description: Any short description or hints that help a GM work this type of challenge into their adventure.
Encounter Type: Social, Combat, Discovery, Transport, etc.
Setting: City, Wilderness, Building, Underground, Ruins, etc.
Goal: Kill the bad guys, Convince someone, Locate object, Protect something
Obstacles/Hazards: Locked door, Enemy combatants, Darkness, Freezing temperatures, Trap to disarm (these take away characters, cause penalties, or otherwise stand in the way of success)
Limited Resources: Only X tries before setting off trap (limiting attempts), Only X torches to see while traveling, Only hold breath for X minutes (time limiting), Only achieve 1 of X objectives (objective limiting), etc.
Failure: What happens if the resource runs out or the obstacles are not overcome. Death? Delays? Bad guys get more powerful? Failed mission?

Posted by Eric Gorman:

Burning library Scenario:

Description: You were told to secure a book from an Abbey (Sciptorium, or anywhere else). Some acolyte runs up before you can start looking and blathers at you. Then some screams fire. You have to race up to the library, kick in the door, find the book, maybe rescue someone, avoid or eat some fire damage ... and get jumped by the arsonists. What the heck?!?

Encounter Type: Exploration/Combat
Setting: Urban
Goal: Retrieve Rare Book
Obstacles/Hazards: Fire, Smoke, victims, Bad Guys
Limited Resources: Time.
Description: No everyone wants you to find the book. Either because other parties want it or because other parties want the material in the book to remain unreported.
Failure: a separate set of encounters to track down the assailants or an unsavory deal with someone the PCs would normally consider an enemy to get another copy of the text.

Reserved