Prison Island
From Sonic Retro
Prison Island is an old military base once used by G.U.N. It is here that Shadow was held in a cryostasis for 50 years before his release by Dr. Eggman. In the game Shadow the Hedgehog, Shadow returns to the ruins of the base.
Purpose
After either escaping from Westopolis through the Lethal Highway on Black Doom's orders, helping Rouge retrieve the Chaos Emerald from Digital Circuit, or recovering the Chaos Emerald from Glyphic Canyon, Shadow warps with Chaos Control to the remains of Prison Island, after which a memory band triggers reminding Shadow that a Chaos Emerald lurks within the depths of the island. Once there, he is instructed by Doom's Eye to clear out the remaining G.U.N. forces. However, Charmy Bee is also on the island, under instructions from Vector to find 5 top secret disks (which he comically and ironically does not know anything about).
Other Locations
Many other parts of Prison Island were visited during the course of Sonic Adventure 2/Battle. These locations include Iron Gate, Prison Lane, Metal Harbor, Security Hall, Green Forest, White Jungle, and Weapons Bed.
Appearance (Shadow the Hedgehog)
Prison Island is now a ruined base, as a result of the 'dark side's' plan to distract the guards, steal the Chaos Emeralds, and blow up the island (See (or play) Sonic Adventure 2). As a result, most of what remains is rusted machinery, which surprisingly still works. Even more surprising is the fact that many plants are growing abundantly across the stage, some of which can be broken for a classic wooden-staff head bashing.