North Zealand and South Zealand are a study in contrasts. The great drama and all the three-star man-made attractions, such as "Hamlet's Castle" or the cathedral at Roskilde, lie in the north, and naturally that's where hordes of visitors go. We don't dispute this obvious choice. If you have only 2 or even 3 days for Zealand, the north is a more rewarding target.
But if you have at least 2 days extra to spare, you can take in all the highlights of South Zealand, as travel times are short between sightseeing targets. Zealand may be the largest of all Danish islands, but it is only about the size of the state of Delaware. Even if you have only a day for South Zealand, you can visit it using Copenhagen as your base. If that's the case, we recommend that you confine your trip to the ancient "witch-burning," medieval city of Køge and the offshore island of Møn, both of which can be seen in just 1 day.
Sjælland Syd (its Danish name) is today called a "land of mist and moods," with its prehistoric monuments and ancient towns. Its "cities" are really overgrown towns, and it is blanketed with rolling farmlands, blighted in places by necessary industry. It is also filled with white sandy beaches opening onto rather cold waters.
The land is also filled with medieval churches and a 1,000-year-old ring fortress at Trelleborg. There are often festivals of fine food and music throughout the summer, and there are seemingly endless sailing clubs, which give the ports a real maritime atmosphere, filled with the heady scents of seaweed and tar.
Before Copenhagen or Roskilde emerged, South Zealand loomed large in history as the seat of the Valdemar dynasty of Danish kings. It was also a power player in the Middle Ages and Denmark's ecclesiastical center. In the 1600s, some of the most epic battles between Sweden and Denmark took place here, especially in the seas off Køge. One of Denmark's greatest moments of shame came in 1658, when King Gustav of Sweden marched across the fields of South Zealand heading for Copenhagen. Once here, he forced a treaty that nearly cost Denmark its sovereignty. Motorists from Køge in the east, heading to Korsør in the west (perhaps to cross the bridge over the Great Belt into Funen), would be wise to steer clear of the dull E20 motorway and follow the scenic and greener Route 150, which will take you through South Zealand's best villages and farmlands.