The Gardeners’ Tower is found vis-á-vis from the palace. Its massive basement dates back to the Middle Ages and was built from residual material from the medieval fortress which stood on the island at the time. The octagonal building above the basement and the helm roof were added in the 19th century.
Today, the tower houses one of the Mainau souvenir shops and also various exhibitions about the Bernadotte family on the upper floor. It’s well worth a visit, because there are some spectacular views of the Arboretum and the palace from the Gardener’s Tower.