The Athena Parthenos Shrine is an underground shrine in Rome where the Romans had kept the Athena Parthenos statue after stealing it from the Greeks. It eventually became the lair of the spider monster Arachne.
The shrine is a massive cathedral-like cavern lit by bronze braziers of magical light like the gods use on Mount Olympus. Under Arachne's control, the shrine's walls are covered in gorgeous tapestries of the spider's own making and the celling is so high that it is lost in the gloom. The shrine is covered in spiderwebs with some acting as supports for the walls, celling and floor. Webs also surround the centerpiece of the shrine: the Athena Parthenos itself.
Due to the hatred from the monsters of Tartarus trying to reach the statue and destroy it, the shrine's foundations have been eaten away over the centuries, leaving a crumbling floor over a chasm leading directly into Tartarus itself.
After stealing the Athena Parthenos, the Romans took the statue and hid it in this shrine underneath Rome. Over the centuries that followed, it became the lair of the spider monster Arachne and the location at the end of the Mark of Athena that Athena's children would try and fail to find. Over time, the hateful thoughts of countless monsters from Tartarus trying to reach the statue and destroy it eat away at the foundations of the cavern, leaving a chasm leading into Tartarus itself below the floor.
In the modern era, the shrine is located beneath the rear parking lot of the Emmanuel Building.
Having been given the Mark of Athena by Minerva, Annabeth Chase embarks upon a solo quest for the Athena Parthenos, eventually leading her to the shrine. Unable to defeat Arachne in combat, Annabeth tricks her into unraveling the Athena Parthenos and creating a trap for herself. Enraged, Arachne summons her children to attack Annabeth while her efforts to break free by shooting spider silk at the walls start to make the cavern unstable.
Having learned of Annabeth's location from Bacchus, the Argo II arrives and blasts the parking lot over the cavern with the ship's ballistae, sending several cars down into the cavern and collapsing part of the roof. A Fiat 500 hits the trap, breaking the floor and sending Arachne down the chasm into Tartarus. Rendered even more unstable by the Argo II's arrival and the unveiling of the Athena Parthenos which unleashes the statue's power, the cavern begins to collapse, threatening to send the Athena Parthenos into Tartarus as well. Leo Valdez, Frank Zhang and Jason Grace work to secure the statue with grappling lines, but Arachne manages to ensnare Annabeth and pull her to the edge of the chasm, dragging Percy Jackson along with her when he tries to save his girlfriend. Unable to pull them up, Percy orders Nico di Angelo to lead the others to the mortal side of the Doors of Death where he and Annabeth will meet them before Percy allows himself and Annabeth to fall into Tartarus.
Moments later, the floor collapses completely, but the Athena Parthenos is secure while Nico and Hazel Levesque are able to get on the Argo II's rope ladder. The silk support columns that Arachne had created all snap and the cavern implodes as the Argo II escapes, burying the chasm to Tartarus in tons of rubble. The mortal authorities are left confused by the sinkhole that is left where the Emmanuel Building parking lot once was, but no one is hurt. Jason, Hazel and Frank return to the scene of the catastrophe, hoping to dig down through the rubble and find a way to save Percy and Annabeth. However, it proves to be futile as the cavern is simply gone.