In a comparison of the east and west coasts of Africa, the book mentioned that prevailing winds are southern on the west African coast. Until improved ship designs in the 15th century, ships could sail down the coast of Africa, but they could not sail back!It must have sucked figuring that out. If you went south too far in a medieval ship, you’d probably never get home. You might try to land and walk back home, but good luck crossing the Sahara Desert.
D&D ships are probably of medieval design, and it is quite possible that, as in the real world, there may be one-way journeys for D&D ships. Here’s a natural way to impose the same kind of walls and one-way doors on the campaign map that exist in the dungeon.
Imagine the easternmost continent of a campaign world has a prevailing easterly wind along its deadly southern coast. Once you go too far, it’s impossible to sail back to the known world. Let’s say that there’s a tempting ruin right on the edge of the point of no return. Getting there requires a ship-based skill challenge. Success means that the PCs get to the ruin. Failure means that the PCs’ ship is caught in the current/prevailing wind and has no way of getting home except by circumnavigating the globe, which will take a year or more. Here is a skill challenge with major consequences for failure! Failing the challenge would change the nature of the campaign, potentially for many game sessions, into a ship-based Odyssey campaign. Failure in this case might be much more interesting than success.
When medieval sailors returned from their journeys, they described the D&D-type monsters they encountered off the edge of the map. What wonders will D&D characters meet on the other side of the world? Everything can be even more exotic than usual. PCs can find magic sites and treasures that would would be game-changing if they were more accessible, but here they’re all guaranteed to be encountered only once.
Rather than treating a circumnavigation like a series of railroad encounters, I’d give the PCs the illusion of control by letting them make some encounter rolls. Here’s what I’d do:
Circumnavigate the D&D globe
Figure it takes 60 weeks, if everything goes well, to circumnavigate the globe. Every week, the PCs roll a d6. On a 1, they encounter an adventure. This will lead to an average of 10 adventures.
Many sea-based encounters (like islands) are avoidable. On the other hand, the PC’s ship probably isn’t stocked for a year of sailing. Say an average ship has room for food and water for 8 weeks. Every week without an encounter brings the PCs closer to half-rations or starvation. Every island is a chance to restock the ship. With 8 weeks of food and a 1/6 chance of an encounter every week, the PCs may well find themselves hoping to sight land.
Next, the DM rolls on the adventure table.
1 Storm: Skill challenge. Failure results in a “Robinson Crusoe” inspired adventure where the PCs try to repair their ship or build a raft.
2 Navigational hazard: Reefs, whirlpool, calm, sargasso sea, bizarre magical hazard.
3 Continent: PCs discover a new continent, which means they probably encounter other shipping, possibly pirates, and must spend extra weeks either sailing around the continent or crossing it by foot.
4 Island of the bizarre creatures: The PCs encounter a PC race that the DM has banned, or something else that doesn’t fit into the campaign.
5 Island of the fabulous treasures: Gems that grow on trees, a miracle crop that would help starving peasants, fountain of youth, all guarded appropriately. Every ton of treasure is less room for food and drink in the hold…
6 Desert island: uneventful chance to restock the ship.
7 Giant sea creature: Sea serpent, kraken, sea titans, giant turtle with an island on its back. May be too badass for the PCs to defeat.
8 Classical adventure: Episode inspired by Odyssey or Jason and the Argonauts. Circe, clashing rocks.
9 1001 adventures: Episode inspired by the voyages of Sindbad or 1001 Nights. Giant roc, island of djinn.
0 Modern (ish) adventures: Episode inspired by Gulliver’s Travels, Prince Caspian, Star Trek: Voyager. Island of giants who try to capture PCs, island of invisible tricksters.