200+ Skies for Unity

The pack includes over 200 skies for Unity provided "as 6-sided cubemaps sized from x1024 to x2048 per-side along with an equirectangular cubemap texture from 4k to 16k in size," according to the description. Each comes with an example scene. 

Features:

• Day, Night, Cartoon, Fantasy, Hazy, Epic, Space, Sunless and Moonless
• Twilight, sunset, multiple times of day, multiple times of night, skyglow
• Many weather and cloud types: clear, overcast, summery, stormy, autumnal, hazy, epic, foggy, cumulus

You can learn more here.