koobas.hobune.stream
Terrain Menu is gone in the MenuBar.
How to find it back? This is really weird.
Unity does't have a terrain menu. Maybe you need to import a package which will add that menu into the editor? (Just like you've imported 2D Toolkit and Easy Save which have added extra menus.)
U can find it in terrain properties in Inspector menu. Click on terrain and later on cogwheel.
You can create terrain from GameObject -> Create Other -> Terrain
