Velvet cave 홈페이지 : http://www.kasteelvalkenburg.nl/default.asp?id=267 Nice and cool in the summer and wonderfully warm in the winter, the Velvet Cave is a permanent 12 degrees Celsius year-round... naturally! Visit the oldest cave (marlstone quarry excavation) in South Limburg... Closely connected with the rich history of the castle ruin is the Velvet Cave, the network of passageways ben..