The Royal Oak (also known as the Big Oak, Millennial Oak or Volkenroda Oak) is a natural monument on the outskirts of Volkenroda, a district of Körner, in the Unstrut-Hainich-Kreis in Thuringia, Germany. The English oak (Quercus robur) is more than 600 years old and has a trunk circumference of about 9.5 meters. The presumed age of the oak was determined by taking drill cores from the trunk and ring counts from a broken branch. It was previously assumed that the location of the oak was an old Germanic Thing site. However, more recent research suggests that the oak grew in a medieval Hutewald forest.
Nowadays, Pentecost services are held at the Royal Oak church services are held at Pentecost. It is owned by the municipality of Körner and has been professionally restored several times over the past hundred years.