i thought i was trought with sightseeing but no. there are always some gems to be descovored. for example the labyrinth. its not exacty in the center but worth a visit. take the green line until mundet and there you are. there is a big garden and a castelike building and, most important, a labyrinth. the hedges are higher than man's hight so you can't cheat. even though it is not realy big you can get confused and kind of get lost. it is big fun.
around it you have romantic gardens and 'grotas' of echo, narcis and ariadne. there is a hades-like canal and well, you should better see it yourself.
what else? it is hard to describe that place properly, see the pics and get some impression of it.