- Cannot be adjacent to another Seastead.
One of the ultimate expressions of human technology, the Seastead is the only man-made structure (or perhaps the first of many) capable of withstanding the force of ocean waves. Although it doesn't become available until the final stages of the game, it can vastly improve the yields of water tiles around coastal and island cities. Its adjacency bonuses work not only on itself, but also on nearby Fishing Boats; what's more, it can be built on tiles that otherwise cannot support improvements. It, along with the Offshore Wind Farm, allows for major development of all coastal cities.
Finally, the Seastead is also good for "reclaiming" tiles that have become submerged due to sea levels rising as the world's climate changes.
By custom, the sea is a place of its own laws, under the control of no nation. This makes it attractive for people who wish to experiment with new models of government, and so the idea of “seasteading” is the creation of new micro-nations at sea. As of the publication of this game, no permanent, sustainable seastead has been created, but many organizations around the world continue to explore the practical implementation of seasteading, whether by creating artificial islands or converting large sea-going vessels (like retired cruise ships) into permanent seasteads.