In the North Sea, near the west coast of the German state of Schleswig-Holstein, about 300 people live on small scattered islets called the Halligen. How do those people get to hear the Bible’s message that Jehovah’s Witnesses preach?​—Matthew 24:14.

The Witnesses travel by ferry to reach some islets. To contact the people who live on other islets, however, a small group of Witnesses use a different method​—they walk about five kilometers (3 mi) across the seabed. How is that possible?

The secret lies in the tides. At about six-hour intervals, the level of the North Sea in the area of the Halligen rises or falls by about three meters (10 ft)! During the ebb tide, large areas of the ocean floor are exposed, and the Witnesses can reach three of the islets on foot.

What is it like to make this journey? “It takes about two hours to reach one of the Halligen,” says Ulrich, an experienced guide who leads the group. “Mostly, we walk barefoot. This is the most efficient and comfortable way to cross the seabed. In cold weather we wear boots.”

The scenery can seem surreal. “You may feel as if you were walking on a different planet,” says Ulrich. “Some parts of the seabed are muddy, other sections are rocky, and yet other areas are covered with sea grass. You see swarms of seabirds, crabs, and other animals.” The group occasionally has to cross tidal creeks, called Priele in German, that form in the mudflats.

Those who make the trek face challenges. Ulrich warns: “You can easily get lost, especially when sea fog sets in. So we use a compass and a GPS device, and we keep to a strict schedule so that we don’t get caught by the rising tide.”

Is it worth the effort? Ulrich relates the story of one man in his 90’s who regularly reads The Watchtower and Awake! “One day, we had so little time that we could not visit this man. Before we departed, however, the man came on his bicycle to catch us and said: ‘Aren’t you going to give me my Watchtower?’ Of course, we were happy to deliver it to him.”