Description In order to play Portal: Prelude you need to have Steam/Portal installed on your system.
Portal: Prelude is an unofficial prequel for Valve's hit title Portal. Its story revolves around the pre-GlaDOS epoch, even before she was plugged in. At thisPortal: Prelude is an unofficial prequel for Valve's hit title Portal. Its story revolves around the pre-GlaDOS epoch, even before she was plugged in.
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