Kratos, sacrificing a Siren
In the Palace of the Fates, Kratos is given the Key of the Ram. Opening the door takes Kratos to the Garden of the Gods and beyond that, to a chamber with two levers operating flame spouts on opposite ends of the wall. Kratos is required to use the flames from the spouts to sacrifice three Siren Widows for the Sisters. Doing so will open a door with the entrance to the Bloody Swim Tunnel inside.