Although Leipzig makes for a long day trip from Berlin, it's worth a visit. It's one of Germany's main music, art, and cultural centers. And what's great, most of Leipzig's attractions are located in its compact city center.
One thing to see in Leipzig is the Völkerschlachtdenkmal (Battle of Nations Monument). It was built to commemorate the Battle of Leipzig in 1813. The monument has a viewing platform at its top, which affords fantastic views of the city.
For architecture buffs, the Völkerschlachtdenkmal is also a good example of Wilhelmine architecture. Its carved figures, including the Totenwächter (Guards of the Dead), evoke German heroism and mythological figures. When I visited the monument a few years back, I felt like I was on the stage of a Wagner Opera.
The monument is currently undergoing restoration, so check to see if it's open to the public. To reach the Völkerschlachtdenkmal take tram line 15 and stop at Völkerschlachtdenkmal.