Dear Monster-Trainers,
in order to "discover a hidden room entrance" you need to
break a wall with the
ability of a monster. While in adventure (on the map, not combat) you can choose between your companion. Press "A" or "D" to choose the monster at your side. You will need to pick a monster with an ability that allows you "
Breaks hidden walls".
First monsters you will collect with such an ability should be "
Catzerker" or "
Yowie".
Full list here:
https://monster-sanctuary.fandom.com/wiki/Explore_AbilitiesYou will find an easy possibility to do this right on the side from the teleport-point (diamond object) of the
Mountain Path. Go to the right and talk to the girl. She will actually tell you, that behind her is a breakable wall. Other walls can be found anywhere in each area, there will be a small fissure in the wall in order to show, that there is a hidden room behind it. Most of them reward you with a treasure or new room.
You can always check your map and compare with this one:
https://monster-sanctuary.fandom.com/wiki/Mountain_Path#Map in order to see, where is a hidden room.
Greetings to all of you!
Let me know if I forgot something.