The Docks are a series of wharves that make up the seaport of the kingdom. Only one ship uses it as its port of call: The Pride of the Watcher.
Every territory can apparently be reached via the docks, despite only two being islands. A combination of river and land travel may explain this oddity.
Monarchs, Knights, and Spies can also board the ship to patrol the seaways to Effenmont, Gastrobury, Ticktop, and Advorton, which increases their loyalty. They may also choose to patrol the high seas, which has no loyalty effect. Merchants can use the dock to trade with other territories for rare items and goods, or as part of their responsibilities. Sims with the Whale Ate My Parents trait can use the docks to "Scream at the Sea" or go Whale Hunting. Spies may occasionally be tasked to "Sail to Foreign Territory".