Fantastic landscapes that resemble seas in form and function but are actually something else are a common element in fictional worldbuilding. These areas may be endless deserts traversed by wind powered sleds, or they may be expansive grasslands where snake-like leviathans lurk beneath the windblown meadows. Even the open skies and space itself can be designed to resemble the high seas with the inclusion of elements like airship pirates or whirlpool-like space anomalies. Below are a few examples of alternate seascapes found in fictional worlds as well as common elements that worldbuilders may wish to include in their design if using them.

Desert seas are areas of rolling sand dunes and a common ‘sea’ in both fantasy and science fiction worlds. There may be fierce sandstorms in these areas as well as great beasts (or leviathans) that burrow through the landscape. Rocky outcroppings may act like islands in this terrain and mesa cities may offer a safe port from the dangers of the deeper desert. Worldbuilders using these seas in their own fictional worlds should consider whether their deserts contain oases which may function like island outposts.

The vast expanse provided by the open skies lends itself to acting like an alternate sea and often worldbuilders including a large sky element will also include other sea-associated elements. Airship pirates may roam the clouds or make pirate ports in hard-to-find locations. Floating rocks may be a type of island or be a kind of hard to navigate ‘treacherous waters.’

Worldbuilders designing whimsical summer camps or lighthearted adventures to a lakeshore will often transform a small lake into a vast sea-like domain. These sea-like lakes may feature old sailors telling stories of the leviathans that lurk in the lake depths, the waters themselves may be dotted with mysterious islands, and there may be pirate treasure hidden in places nearby.

Grass seas contain two areas, a grass ‘canopy’ where magical boats may be found floating, and a sheltered deep that may hold a labyrinthian maze of grass tunnels and avenues. Grass seas may be home to giant snakes or other beasts.

Seas of glass are areas where some great force of heat (either magical in nature or an orbital bombardment) has heated the surface of a world to such a degree that it has turned to glass. The inhabitants of these worlds (or those that survived the transformation), may use sleds to traverse the expanses. Clear glass may reveal the ruins of buildings trapped within the depths below. There may be storms that ravish the landscape.

Similar to seas of glass, oceans of ice are areas where an expanse of solid ice acts as a still plane of water to be explored. Rather than ocean storms, there may be blizzards and icy gales. Rather than boats sailing through the water, there may be wind-powered sled skating on top. Of course, adventurers navigating these lands should be wary of crevasses large enough to swallow a person whole.

These alternate seas always feature a vast expanse of some material which resembles or functions like ocean water (or in the case of space, a vast expanse of nothing). Often there will be some method of traversing this landscape in a boat-like vessel or vehicle. These craft may be airships, wind-powered sleds, hovercraft, magical floating frigates, or some other ‘ship’ fit for this environment. These boats may need a harbor, so consider what settlements exist on the ‘coast’ of this sea (and what defines the coast in the first place). There may also be islands within this sea, so consider what terrain features or other elements may take on that role in your own world (mesas, asteroids, floating rocks, etc.). Along with frequent travel there may be trade routes, and expensive trade goods means there may also be pirates and piracy (or pirate treasure and treasure maps).

Pirates are not the only dangers that other seas commonly contain – many of these landscapes include their own forms of leviathans. Massive storms and whirlpool-like phenomenon may also pose a threat to those sailing these ‘waters.’ And if including dangers such as these, it may be worth it to consider shipwrecks or whatever may be your worlds version of a wrecked vehicle. There may be lighthouses to help minimize the dangers or shipwreck towns full of the less fortunate.

As for the people that live in these regions, they may be sailors (or the fantasy world equivalent), fishermen, lighthouse keepers, or other working people or tropes that fit with a more oceanic world.

Alternate seas have many elements in common and many of these elements are derived from things that may be found in fantasy seas. If you are designing your own other sea, consider incorporating oceanic elements and adapting them to fit your world.