In your Landscape window click on Modify Terrain.
Click on the Canyonize button 3 times. Let it do its thing in between each click. Then Click Close.
In your Render Control window click on Render Preview.
Move your camera around until you see a good "sunset dip" near the center of your image.
Don't forget to click your Render Preview to check how it looks.
You might also want to change that Fixed Height number.
Want some water?
Open your Water window.
Change the Level number to 0.m then click on Update Maps.
Do you see blue areas in your Landscape window?
If not raise the number, if it is too much water then make it a negative number. Just play with it until you find a setting that you like.
Don't forget your Render Preview.
When you have the water to your liking click the little x in the top right of the Water window.