I base these missions in Fallout New Vegas.
These missions consist of investigate places after reading a note or listen to a NPC. I will explain better with an example:
1..The players find a note in a cabin in the woods. The note talks about a key that opens a hidden bunker in the cabin. It will not activate any mission or mark reading this note. So in here plays the players’ curiosity.
Hi Maria. Don’t be angry, but I lost the damn bunker’s key again. I know, I know… I should put it in a keychain… Sorry. I go to Anton’s shop to see if I can get a new key. I love you. Be safe and close the doors at night. Remember: today put the red light. I don’t want to have more problems with the damn Rite again…
2. Now the players can try to find the key of the bunker going to Anton’s shop. In there, the owner, an android called Anton, will tell to the players that Suso took the key and come back home and that that place is very dangerous because of the Rite that lives nearby.
3. At that moment, the players will be able to go to investigate the surroundings of Suso and Maria’s home.
4. Then the players will discover the Rite that lives in there. Now they will be able to investigate the Rite using stealth or killing everyone.
5. The players will discover the corpses of Suso and his daughter Maria. In Suso’s pocket, the players will find the key to open the bunker.