Although more people drive or take buses and trains over new bridges spanning the waters, ferries are still a good way to explore Denmark and Scandinavia, especially if you have a rail pass. The Eurail Scandinavia Pass, for travel anywhere within Scandinavia (Denmark, Sweden, Norway, and Finland), is valid on some ferry crossings.
DFDS Seaways sails from Harwich in the United Kingdom to Esbjerg (20 hours) on Jutland's west coast. DFDS also sails to Oslo from Copenhagen. Fjord Line is another company with service between Denmark and Norway. Scandlines connects Denmark with Sweden and Germany.
Vehicle-bearing hydrofoils operate between Jutland's Ebeltoft or Århus to Odden on Zealand; the trip takes about 1 hour. You can also take the slower (2 hours, 40 minutes), but less expensive, car ferry from Århus to Kalundborg on Zealand. From there, Route 23 leads to Copenhagen. Make reservations for the ferry in advance through Mols-Linien. (Note: During the busy summer months, passengers without reservations for their vehicles may have to wait hours.) The Helsingør/Helsingborg vehicle and passenger ferry (Scandlines) takes only 20 minutes.
DFDS Seaways. Dampfærgevej 30, Copenhagen, 2100. www.dfdsseaways.dk.