How to Create an Unlimited Number of Unique One-Way Portals

One-way portals are cool, but there are only six colors, so if you're designing a large map it's easy to run out of them. Here's how to create as many one-way portals as you want:

• Make a path of water between the entrance and the exit at least two tiles wide. The water does not actually have to be passable by ships; e.g. there can be mountains on top of it.
• Place your two Ferries.
• Place the entrance tile of another adventure object on top of the Ferry that you want to be the exit. This makes the exit inaccessible from land.