The Seaside Harbor Light is located on a circular platform on Bygone Island's southern coast. The structure resembles a lighthouse, with a circular entrance, a Crystal Lock in front and three rows of cyan orbs adorning the bottom and top. When activated, four small pillars extends from the top and a column of light shoots into the sky. Due to being over a millennia old, it has cracks in the surface and vines growing on it.
Inside the Seaside Harbor Light is a teleporter that leads to the Sky Citadel. However, it can only take two passengers; after that, it becomes unusable.
Sonic Boom: Rise of Lyric
The Seaside Harbor Light was seemingly created by the Ancients at least over a thousand years ago.
In the present day, Team Sonic came to the Seaside Harbor Light to find the final Chaos Crystal. Using the Twilight Crystal, the team unlocked and activated the Seaside Harbor Light, but when they attempted to use its teleporter to reach the Sky Citadel, only Knuckles and Amy got through it. As such, Sonic and Tails had to use the Tornado to reach their destination.