Locked gate in Valley of a thousand rivers

[Zingo]

Can someone help me answer the two below listed questions

1. How do I open the locked gate in Valley of a thousand rivers?

2. Where can I requite some green dragons? I have read some hints in the forum but I can find the cave you are referring to (next to the lighthouse…). I have found the Elf underground cave on a island and killed all dragons in the cave but I can’t find the merchant. I have sailed through all elf costs but I can’t find the cave you all seem to refer to.