Off the coast to the north of the Prytaneum sprawls an overgrown island. Unlike most of the grounds, which are tended-to and curated, this island seems more or less untouched: wild and overrun, it is clearly marked as off limits for all Chosen, warning signs making it clear that it's dangerous.
This is because anyone who enters the island becomes trapped within its bounds.
This is because this is the Prytaneum's prison -- and here is where the Heroes capture all those who they cannot send into Hades's care, immortal prisoners held on the grounds for safe-keeping.
