level detector(scene)

@syclamoth just answered this in your other question Make a character be on another scene earlier...basically...

As for making a scene for every quest, I guess that would depend on if you're only making a few quests, or if you're making a gargantuan game like The Elder Scrolls . I wouldn't imagine making 5,000 scenes so that each quest would have it's own level would be a good idea, or if it's even possible to have that many scenes in a build ; and besides that, who would want to play a game that has 2 hours of play-time and 3 months of loading levels in-between?

If you go with a scene per-quest, @syclamoth's answer on your other post is how you'd transfer your character from scene1 to scene2.

If you go with transporting your character to quest-start in the same scene, use an empty game object as a spawn point (can make it look better adding some kind of teleporter-base or whatever, but still use an empty object for the spawn-point since your base would probably be on the ground, and if you teleport to that position your character would be stuck half-way in the dirt...) and simply make your character "go" to that point by changing the transform.position.^{Note: This will look like crap without doing some other things, maybe a screen-fade to hide your character suddenly being in a different place ; stuff like that... but whatever.}

Or, you could just let your guy talk to the quest-person, start the quest, and let the player find their own way to the quest-area.