In this paper I will deliver the story of a planetarium conceived by a wealthy burgomaster of Rotterdam in the seventeenth century and now on display in the Museum Boerhaave. I will firstly sketch the origins and life-story of this large orrery, describing how it stayed unknown during its early years and only became famous after it was transferred to Leiden. It was there that the instrument was given a name: The Leiden Sphaera.

In the second part of my talk I will describe the restoration of the planetarium carried out by the Boerhaave staff. I will discuss not only the details of this work, but also some of the new information that appeared during the dismantling of the object.