There are three old towns you can visit during one day trips from Leipzig.
I found Merseburg the most beautiful of the three but maybe it has to do with the fact that it was the first one I visited. The impressive palace complex, the carved tower staircase, the gardens, everything was so enchanting and sort of magical.
Weissenfels or Weißenfels as it is written in german, is a typical small city, rather sleepy and boring. Its Neu-Augustusburg Castle is probably the most interesting site, and contains a church which is a real gem. Another attraction of the Castle is the shoe Museum which unfortunately was closed on the day we visited the city.
Last but not least is the city of Naumburg with its great Cathedral or Dom, a majestic building which we saw only from the outside. But this was a personal choice, or rather the result of a certain dispute between me and my other half who thinks that churches shouldn't be visited like museums with a cetrain ticket (in this case a very expensive one) but should be open and free for anyone who would like to enter and pray. I have tried to defend the opposite side by saying that churches are monuments, too, and need funds but somehow I have a weaker character. That's how I didn't see the interior of the Naumburgerdom, that's how I didn't see the interior of the great church of Bad Doberan during an older trip.
But as I mentioned already, this is a personal conflict which I have to solve mostly with myself.