Mainz-Laubenheim(Germany)
Editor of DKAR 1:127 suggests location is Nubenheim, settlement near Mainz. German Wikipedia and Mainz-Laubenheim website (http://www.mz-laubenheim.de/node/2) identify Nubenheim as former name of Mainz-Laubenheim.
Melk(Austria)
Place in DKAR 1:212 described as at meeting of Pielach and Danube rivers. Geo-located to Melk, nearest modern settlement.
Nahe (river)(Natural Landmark)
Left tributary of the Rhine.