The heart of the Flower garden is an octagonal pavilion called the Rotunda built between 1666 and 1668 according to a project by Giovanni Pietro Tencalla.

The building was designed as a regular building open to all sides with a central hall which is followed by four artificial caves (grottas) and four lounges (stone rooms). The interior is decorated with rich sculptural, stucco and painted decorations. According to the period fashion the entire building was surrounded from the outside by laurels and pomegranates.

From 1669 the architect Tencalla was focused on the interior decoration of the building - the painting decoration was entrusted to the Tencalla´s workshop. On the other side the statues of fauna, fountains in grottas and allegorical figures of the Four Seasons was made by the sculptor Michael Mandík. The rich stucco decoration was created by plasterers led by Quirico Castelli. A stone mosaic was laid on the ground. All decorative elements of the Rotunda are connected by the motif of water - the source of life and the place of purification.