Okay, so I have made this simple Environment in Unity.
To create a Cubemap (to capture your Environment into a Cubemap) you need to download this Script! After you download it, create the Editor folder anywhere in your Project tab and put a RenderCubemapWizard.cs inside that Editor folder.
Create an Empty GameObject in the Scene.
I called it Render Position (you can call it whatever you want). Changed it’s position to the center of my Environment. This will be the Cubemap capture position.
Create a Cubemap. Inside Project tab press RMB, select Create > Legacy > Cubemap.
It will create this grey Cubemap without any textures applied. I called it Cubemap_01 (you can call it whatever you want).
Select Cubemap_01 and enable Readable (Very importatnt)! This will allow the scripts to access the pixel data of the cubemap. I also changed Face Size to 512 (Width and Height of each Cubemap face in pixels. The textures will be scaled automatically to fit this size).
Now go to GameObject > Render into Cubemap
This window will pop up
Add Render Position (Empty GameObject we just created inside the Scene) to Render From Position. And inside the Cubemap slot add Cubemap_01 (Cubemap we just created inside Project tab).
Now we have a nice Cubemap created.