When exactly is the difficulty level of a location set... when you initially "discover" the location, or when you enter it?

I haven't been able to find a definitive answer to this question. In fact, I've read posts from people who say they have discovered a high-altitude dungeon without entering it, only to return later on in their game and breeze through it with ease.

Furthermore, if the difficulty level of a location is set when you "enter" it, what does that mean exactly? For dungeons and caves it's straightforward, but what about castles, temples, and other outdoor above-ground locations?

I'm still fairly early on in the game, and many quests demand that I travel large distances over previously unexplored terrain to get to a certain destination. I don't intend to explore every single location I discover along the way (I'd rather save them for later, to be explored as part of a future quest), and the last thing I want is to ruin my game by inadvertently level-locking these locations as I travel.

Difficulty seems to be set upon discovery, but I can't say for sure.

I dno
but I do know when you start worrying about it too much you might ruin the experience in the process
it might not be optimal and worth arguing, but if you're playing the game and constantly have to avoid discovering dungeons and worry about level locking
the whole experience changes from, hey cool a cave let's see what's in there into something like when did I discover this cave, do I want to enter it now or save it for later

at least that's how I see it
too much meta-gaming (playing the mechanics as opposed to playing the game world) can really ruin the experience for me

Thank you for the replies. A very valid point about ruining the experience by worrying about it too much. I'll find a compromise that still lets me enjoy the game.