Wonder Boy in Monster World/Secrets

Monster World has many secrets that can be unraveled. There are lots of hidden doors and treasure-chests to be found by Shion.

Secret caves
There are two secret caves inside the cliff at the far right of Maugham Desert. In order to get there use the teleporter in the pyramid to take you to the mountain area. Once there, head left until you reach the cliff edge. Fall off the edge while hugging the right wall (keep the D-pad held firmly to the right). You'll end up inside the hollow wall that leads to the first of the secret caves (this one has 2 units of Shield magic). Repeat the process by exiting and continuing to hold right, hugging the wall, to reach the second secret, containing a 2 unit upgrade for your Power magic.

Pygmy areas
There a 2 secret places which you can enter after you're turned into a pygmy. The first one is in the pyramid. You can reach the pyramid by using the teleporter near Begonia. Once inside go to the room with the treasure chest and the secret door. Now you're able to walk to the left where you'll find a charmstone and lots of gold. There's also a heart here, just walk through the left wall in the room with the 4 doors. The other secret area you can enter as a pygmy is in the ruins near Lilypad. From the start, walk to left, decent the ladder and go left. Here you'll find another heart container.

Secret door in the pyramid
Inside the pyramid there's a seemingly inaccessible door beside a chest, with no visible entrance. The door is hidden. Go right, near the wall (as shown in the picture) and press Up on the directional pad to enter the hidden door. The secret chest increases the MP maximum of all your spells - (Fire Storm, Lightning, Earthquake (Explosion if playing the TG16 remake Dynastic Hero), Shield and Power. If you're missing any of these spells, they'll now be acquired.

Secret doors in the sea
There are 3 secret doors in the Monster World sea near Alsedo. They will all lead you to treasure chests with money.

Minor secrets
There are lots of spots where you can find gold. For example on the tree trunk in the beginning of the game and left from the ladder near the tree at queen Eleanora's hideout. You can also try to jump near the arrows which point up.