Roskilde Cathedral is inscribed on the UNESCO world heritage list. It is a unique and beautiful medieval cathedral. The Viking kings Harold Bluetooth (d. 985) and his son, Sweyn Forkbeard (d. 1014) conqueror of England is buried here. Almost 40 kings and queens of Denmark are buried here.
http://www.visitroskilde.com/ln-int/roskilde-cathedral-world-heritage-gdk619579