Big Mountain

I wanted to created a descent size map 3000x3000 or less however where i am hitting the wall is when i am trying to create a large mountain and i am struggling with height of it. Even when i try to max it it does not seem that high. Have anyone attempt to create a huge mountain? Even world of warcraft achieved it since you get get on top of some and you can tell there is a long way down from them. How do you do it? Need a prefab and blow the height on it or how would you approach this?

I tried to mess around with Gaia to generate my terrain. It just seems that no matter what i use the mountains still look somewhat small. or not as high as i would want them to be.