Even if you bought the guide, this can be trying on your patience. The secret room found after completion is also where I found Tisinge later in the game.
So here are some hints. Okay way past hints. But if this doesn't get you past the monkey puzzle... Well, lets just say that some quests in the future are gonna get tough.
1. Get to the floor where you see a red monkey walking around. Even if you have trouble seeing the color red, the monkey looks very different than the others.
2. Get within visual distance of the red monkey and then remove the anti-monkey bandana you should be wearing.
3. Touch the monkey and he will steal some money and run away. Don't worry, it's not a lot.
4. Put your anti-monkey gear back on and leave the dungeon. Just exiting the screen is not adequate.
5. Re-enter the ruins and find the red monkey again. He is always in the same general area on that floor. Remove the anti-monkey gear and again touch the red monkey.
6. If Caius says something like "He didn't steal from us that time" then you know you have suceeded. I only had to have gold stolen once, but someone else reported they had to repeat the exit/enter process more than once.
Then, follow the monkey that disappears through the north wall of this room to find the secret room. This was harder for me than expected, so you might be hitting the wall a few times if you didn't pay attention to exactly where the monkey went.
Sorry for spilling the bananas, Indi, but it's in my nature to help people succeed.