Sebastian Lague has good videos on Unity projects. You can check out his planet generation series at https://www.youtube.com/watch?v=QN39W020LqU&list=PLFt_AvWsXl0cONs3T0By4puYy6GM22ko8. You get to create procedural planets, and the end result is pretty fun I think.
You can also go to the Catlike Coding blog for more advanced stuff: https://catlikecoding.com/unity/tutorials/.