If Spiegel had initially intended the Belvedere as his burial site, he changed his plans by 1783 at the latest. In that year, he stipulated in his will that his remains should be interred "in the burial ground on the Spiegelsberg" and commissioned the construction of the mausoleum, which was presumably completed at the end of 1784, relatively shortly before Spiegel's death in May 1785.
Gleim wrote to Anna Luisa Karsch (poet, 1722-1791) on October 14, 1784, "He is working very diligently on his burial site near the pine grove. It may well cost a thousand thalers, the mausoleum that will one day enclose the body of the dear old man."
A stone staircase forms the entrance to the hexagonal building, topped with a round dome. The resting area is enclosed by a surrounding iron railing. Originally, an urn stood on each side of the entrance on the pillars of the gate. The remaining pillars were decorated with large spheres.
Above the door, the statues of Saint Lawrence on the right and Saint Stephen on the left watched over the peace of this place.
Inside the mausoleum, in front of a memorial plaque, stands an iron sarcophagus whose inscription bears Spiegel's name and dates of birth and death.
The cathedral dean was buried here in 1785, but his remains were transferred to the family burial ground in Seggerde in 1811.