Demon Fall Canyon

This place might not be that hidden but I think it's a cool place and I found it when I was questing in Ashenvale for my Loremaster Achievement.

It's possible to go here by both flying mount and ground mount, and both Horde and Alliance can go here.

In this dark and creepy canyon you might come across a stone. Click on it!

It will open a little window where you can read that this is in fact a stone raised to honor Grommash Hellscream when he fought Manoroth. This is a kinda cool place and if you haven't visited it already, do it!
Hope you'll all have a great day, love Emma♥