A very nice site about the old tp atderu:
http://www.zollgeschichte.de/monatskarten/11_98.htm
To continue: click on Dreikaiserreichsecke. Lots of old postcards.
The site is about the history of German customs, and is extremely worthwhile. I haven't had a proper
look yet, but it looks promising. Also the old qp bedenl+Moresnet is there! Well, the monumental
threesome at Dutch border marker no. 1 that is.
The Ile de la Conférence looks very nice at
http://cgpa.org/ge64cgp6.htm . It is the last photo.
This site is all about the Pyrenees treaty.
Peter S.