Historical clue formulations

• German industrial region — 2022-08-30
• Germany's largest urban area — 2021-08-21
• German industrial valley — 2021-05-31
• River through Dortmund — 2019-10-06
• European coal center — 2019-09-14
• German industrial region — 2017-10-04
• Region in western Germany — 2016-12-22
• Germany's ___ Valley — 2016-06-07
• Tributary of the Rhine — 2016-03-13
• German industrial locale — 2015-05-11
• ___ Valley, European steelmaking region — 2015-04-13
• Germany's ___ Basin — 2014-12-21
• German coal region — 2014-06-24
• German coal region — 2013-11-04
• Essen's river — 2013-10-09
• Germany's ___ Valley — 2013-07-08
• European coal center — 2012-09-11
• River to the Rhine — 2012-03-28
• River to the Rhine — 2011-08-24
• German region occupied by France and Belgium from 1923-25 — 2010-02-14
• Essen's region — 2010-02-11
• Mülheim an der ___, Germany — 2009-04-05
• Essen's region — 2009-03-31
• Arnsberg is on it — 2009-03-14
• German industrial valley — 2008-04-14
• Essen's basin — 2007-07-08
• Where Essen is — 2006-07-04
• Duisburg's locale — 2005-01-16
• Essen's river — 2004-02-15
• German valley — 2003-12-25
• Essen basin — 2003-05-14
• German industrial valley — 2003-05-13
• German industrial region — 2002-07-28
• European coal area — 2002-03-28
• Where Wuppertal is — 2001-12-21
• Remscheid's region — 2001-05-11
• Essen's region — 2001-02-08
• River crossed by Allied forces in February 1945 — 2000-12-01
• Essen's river — 2000-09-17
• German industrial region — 2000-08-28
• River to the Rhine — 1999-11-05
• German industrial valley — 1999-11-02
• Essen basin — 1999-06-16
• German industrial locale — 1998-11-16
• German industrial region — 1998-01-13
• Essen's river — 1997-11-25
• German valley — 1995-01-25
• Krupp family home — 1994-02-01