Mainz-Kastel, Train station

Meet at the Bahn.de parking lot immediately behind the Mainz-Kastel Bahnhof. (NOT Mainz!)
From Frankfurt:
Take A66 to B455 in Wiesbaden.
Take exit 6-Wiesbaden-Erbenheim to merge onto B455 toward Mainz-Kastel/Wiesbaden-Erbenheim-Süd
Follow B455 to Rheinufer
Go through 1 roundabout
At the roundabout, take the 3rd exit onto Philippsring/B40
Turn right onto Rheinufer

 GPS:  50°0′25″N 8°16′57″E