Maulbronn is still actively in use, all these hundreds of years after construction, as a school, so parts of the complex are off-limits to visitors. However, enough of it is open so that you can get a good feeling for what life was like in the 12 and 13th century monastery. I like the church especially, but it was very interesting to see the warming room (the only room in the monastery that had heat in the old days) and the dining halls.
We walked around outside the north wall of the monastery and around a small lake which I believe was created by damming a stream during the monastery's period of active use. Good half day trip.