We actually have, the problem is that if we do that, the Viking tour picks up at Speyer dock as we dock and goes straight to Heidelberg. If we did that we would miss a couple of the sites in Speyer, such as the Romanesque church. We also considered just DIY, but we’re uncomfortable trying to get a train from Heidelberg to Rudesheim (not a direct shot) and don’t have a firm time on when the boat moves, just know it’s early afternoon.