Prism Gates are the gateways that Shadow Man encounters in Liveside after defeating 3 members of The Five; Jack the Ripper, Avery Marx, and Victor Batrachian. They are opened with prisms and lead to different areas of the Asylum Engine Block.
As stated in Jack's Journal, the prism gates are intended for the reception of Legion's dark soul armies. Originally, Jack planned to have 5 of them built; one for each member of The Five. After the destruction of the The Asylum at the hands of Shadow Man, the Prism Gates were destroyed alongside their surrounded areas therefore preveting any other Deadside Asylum creatures cross to the Liveside.