When was Chapter 1 of the Source Engine mod "Underhell" released?

Chapter 1 of the Source Engine mod "Underhell" was released on September 1st, 2013. This marked the initial release of the mod, which introduced players to the immersive and intense narrative-driven experience set within the source engine. Since then, Underhell has garnered praise for its atmospheric environments, engaging gameplay mechanics, and compelling storytelling, making its September 1st, 2013 release an important milestone in the history of the mod.