Tutorial] Make your own skybox for CS:GO - 3D - Mapcore
2D SkyBox tutorial - Mod DB
Hammer Editor Tutorial - Adding and Changing Sky / 2D Skybox and Global Lighting - YouTube
3D Skybox Tutorial - Mod DB
Guide] Seamless 3D Skyboxes | TF2Maps.net
Asd417's 'Seamless' Skybox Tutorial | TF2Maps.net
TUTORIAL] Making a cool 3d skybox. | TF2Maps.net
Skybox Optimization - Valve Developer Community
HL:A 3D Skybox Tutorial in Under 4 Minutes: hammer
2D SkyBox tutorial - Mod DB
Tip] When your 3d skybox City is too dark because of lighting angles, don't add more lights - Use a textured surface to bounce your lighting! : r/csmapmakers