Mushrooms or eggs or crates will NEVER respawn at the place which your eyes can't see. (e.g. inside the woods)

And you will NEVER find them inside the town or military camp or enemy bases except the surrounding area. So don't search these places.

They usually respawn at the edge of woods or plain.

NOTE: In order to refresh the map, you must complete the game first.

Defeat the dark lord and report it to king. Don't worry, the game will not end. You can click the PLAY button from main menu and continue your progress.

When you sleep in the game (or try to exit to main menu), all the positions of mushroom and egg and crate will be changed. In the other words, they will respawn randomly.

So you can find a hidden object very easily. Because it maybe respawn at an obvious place.

You don't need to check every part of the map or click everywhere. That's a stupid way.