of the strongest positions of Upper Brittany. The castle has been the scene of much fighting—including being badly damaged by fire in out-of-control riots in the forest during the Revolution in 1790—and has passed into the hands of several families. The mansion at the site now houses the exhibitions of the Centre de l'Imaginaire Arthurien (Center of the Arthurian Imagination). Adjoining it is a pond where, according to a local legend, the Lady of the Lake Viviane lived in her underwater crystal palace. Château de Trécesson Located outside the village and the forest, immediately in its extension to the southwest, this castle was rebuilt in its current state in the 15th century. The most famous of the legends associated with it is the one of the (of "white lady" type), which, unusual for the region, has no Arthurian connections but instead seems to be inspired by a true story. Biological station The biological station of Paimpont, under the University of Rennes, was built in 1966–1967; its buildings accommodate about 70 people. The forest and its varied environments provide a framework for university biology courses as well as student and foreign researchers. Although the first researchers extensively studied moor ecology, soils, and hydrology, other works concern subjects far removed from the local biotope, such as the behavior of primates. Megalithic sites Hotié de Viviane The Hotié de Viviane, also called the () or the (), it is a funeral circle of stones dating from about 4,500 ago. It is located near the Val sans retour and has been known under this name since 1843. Tombeau de Merlin In the northern part of the forest is the "Tomb of Merlin", a remnant of a Neolithic covered dolmen structure. The site was largely destroyed with dynamite by treasure hunters after it became associated with the Arthurian figure of Merlin in 1889. According to the legend, having seduced Merlin, Viviane imprisoned him in an invisible prison, and then locked him in a tomb: Merlin, having lain down in a pit, had two enormous stones cast down on him. Today, it is an important site of Neopagan pilgrimages. Visitors to the site might leave flowers and a note to Merlin, often with a wish, or some kind of devotional object. The () is a water hole near the Tomb of Merlin. Also nearby there is an old tree known as the . Tombeau du Géant