I was doing the quest for Barnabas to clear the prison beneath the town and to my surprise i incidentally destroyed a wall revealing a treasure chest and a load of loot. So, like this, i guess there are a ton more. Anyone has a list maybe of the secret places so that i don't miss one?? ;)

This might help too. Great web based, scrollable world map for Grim Dawn. Has notes on lots of interesting in game stuff like chests, dungeon entrances, waypoint locations, shrines, rare monsters and so on.

http://the-maphack.com/index.php?page=2

Note: I wouldn't use it on the first play through of the game, but it's nice to use if you're stuck on something or you're doing a second run through trying to find things you missed first time around.