This is a paid asset, but now you can download Beautiful Sky for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
Beautiful Sky v1.0
This is a stylized skybox pack contains 30+ stylized skybox. If you are making stylized or cartoon style games, these skyboxes may help you quickly improve the quality of your game.
• Contains 30+ stylized skyboxes.
• All skyboxes are stylized, including day, night (with and without moon), cloudy, clear,
overcast, and several low-poly style skies.
• All skies are in 4K (4096*2048) resolution.
• Suitable for any game.
• If you are using stylized or cartoon type materials in your game, these skyboxes may help you quickly improve the quality of your game.
• The scenes and models used in the video for demonstration are not included in this package, This skybox package does not contain any models.The video just show you how to use these skyboxes in a real project.