In the walkthrough that i'm following, it says about a secret in the bear cave in Valewood. Where is it???

Are you serious? Surely this game is not for you if you can't find that. And following a walkthrough, too? I'm confused.

Northwest corner of the Valewood map. You might have walked past it without realizing you could enter. Remember to press Tab often to highlight interactables.

The bear can be a tough fight at lower levels.

Maybe it's talking about a hidden cache (the kind that's visible in scouting mode if you pass a stat check)? I can't remember whether there's one inside there or not.

A bit of searching suggests the guide is probably http://game-maps.com/PoE/Map-Valewood.asp and the original source is https://disqus.com/home/discussion/gamemapscom/valewood_pillars_of_eternity_walkthrough_with_maps_game_guide/ -- which just says 'There is a secret inside the bear cave' without elaboration.

Oops, I guess I misread the question.

Yes, there is a hidden cache there.

@OP: As VanishedOne said, you must to enter scouting/stealth mode to discover hidden objects. There are a lot of these in the game, so be sure to give each room/area a quick check for secrets and traps.

I seem to recall that there was a purple "secret" to be found in that cave. It's been a while, so I may be confused about it. But if so, you might need a few points in the mechanics skill to find it. In any case, you will have to be sneaking to detect it.

(On the other hand, if I'm wrong about it being there, then just ignore my silliness. Or don't. Because that's how you will have to find anything hidden in the game.)

sneaking mode and high enough perception is what you want.

Yes but what's this secret???? Is it that cache? If yes, i already found it.

Either the cache, or what you learn by inspecting the corpse. Depends of what you call a secret.