A magical artifact that appears in at least one very popular fantasy RPG. The folding boat is similar in concept to a portable hole, a bag of holding, and various weapons that fold up, collapse, or otherwise disappear into negative space. The artifact manifests as a full-sized boat of various appearances (raft, skiff, yacht...) which folds up into a small, flat paper item (or an origami boat, or a parcel, etc.).

The important thing about this is it allows you to keep your large, unportable, unwieldy transportation with you at all times.