Jean,
the last photos in the youtube video are not mine 
but the others 
There is a liqueur cellar, you will find it on GE (or a map) at 50°47'43.81"N, 7°12'42.21"E. At the end of 1944 the inhabitants of Siegburg dug three protective tunnels into the hill at about (50°47'47.74"N, 7°12'34.96"E),(50°47'45.32"N, 7°12'32.74"E) and (50°47'41.31"N, 7°12'33.693"E), more than 60 meters deep. Others say one tunnel was at the east side of the hill. There were no sanitary installations at the tunnels, only a privy near the entrance. The hygienic conditions, typhus and other diseases in the tunnels were very poor and made some families look for shelter in their own cellars in 1945. A contemporary witness told our newspaper that his mother had decided to die at home, if necessary.
In 1947 the tunnels were filled up.
The cemetary of the friars is at (50°47'43.07"N, 7°12'34.91"E), and the rose garden at (50°47'47.45"N, 7°12'39.65"E).
@Marion: Is there a way to load kmz files into the forum? Is there an easy way for photos without loading them up elsewhere before?
Christoph