Stock Photo - 10 September 2023, North Rhine-Westphalia, Münster: A restorer stands at the ruins of the Romberger Hof in Münster on the Open Monument Day and measures the time on a test tube filled with water. With the help of this technique, the restorer measures the absorption behavior of the Baumberger sandstone. ""Open Monument Day"" - with nationwide opening in Münster. Münster plays host in the 375th anniversary year of the Peace of Westphalia. Around 5500 open monuments nationwide and, in some places, the opportunity to enter otherwise inaccessible historic buildings are intended to attract visitors. Monument Day is also celebrating its 30th birthday with a record number of events. Photo: Guido Kirchner/dpa. - Münster/North Rhine-Westphalia/Germany