The Mountains of Zar'roc part 2: Mallenoux Caves

And so, Zanik and the adventurer set out on the boat that would lead them into perilious journeys.
It was great, feeling the wind in your face, watching the blue water spray around the boat, smelling the salty sea. Zanik asked "So what's our next desination?"
"Look," replied Forono, showing Zanik the map, "That Island there," Pointing at a small island on the map. "What's it called?" Zanik asked.
"I think it's called Mallenoux, it was named by the guy who founded it, er, Mallenoux."

So, the boat steered on to the small little island, and Zanik and Forono leapt off. "Apparently, there's a cave with a strange sort of treasure inside." Forono said.
"Ok, then, let's go!" Zanik exclaimed, rushing in.
"Wait!" Forono shouted. "You need a weapon. Here's a normal sword to start of with."
Zanik accepted the gift and they both walked into the cave, armed and ready. After fending off a few creatures, they finally got to a stone wall. Forono pushed it, and inside they saw glittering pieces of gold. Forono was about to store a big bunch in his pockets when Zanik said: "What's that, over there?" Pointing at a strange thing inside a glass casing. The two walked up to it and opened the glass casing. They saw a gleaming Diamond. It was coloured red. Zanik took it, then suddenly, a dark flying creature appeared out of nowhere! It then screamed in a piercing voice. "Give me that!"
Zanik was about to hand it to the beast when Forono stopped him and said: "Number 1 rule in adventuring: Never give a scary looking beast a valuable diamond!" And they both ran, but then they exit was blocked off! So the two had no other choice but to fight the thing. They both drew their swords and sliced them at the beast, but nothing could kill it. They kept attacking, but the beast never died! Just then, Zanik spotted the beast's weakness; the eyes, that was the only facial features the thing had. So Zanik aimed, very carefully and stabbed the beast in the eyes, then it vanished into dust. The door opened, and the two escaped. They ran out of the cave, and ran to the boat. "Where next?" Asked Zanik, as they both jumped on the ship. "To a place called Harinathea, it's a big town on an island there, and hopefully someone will tell us about that Diamond you found."