St. Goar is a narrow riverside town built beneath a large castle, and the castle is what you came for. Burg Rheinfels rises on the hill above, a huge ruin with tunnels and cellars that is the largest fortress ruin on the Middle Rhine. It was built in the thirteenth century by the Counts of Katzenelnbogen to collect tolls from passing ships, and it grew into a vast complex that withstood a siege by French troops in the seventeenth century, only to be blown up by the French in 1797 after they took the area. Walking through the underground passages with a torch is a bit like exploring a stone beehive.
Opposite, on the east bank, stand Burg Katz and Burg Maus in the neighbouring town of St. Goarshausen, whose names, Cat and Mouse, are the result of an old joke about the Katzenelnbogen counts. The two towns are linked by a car ferry, which crosses the Rhine at regular intervals and lets riders switch banks without a long detour. It is a small pleasure, riding onto a ferry with the whole Rhine Gorge around you, and the crossing takes only a few minutes.
The town takes its name from Goar, a hermit of the sixth century who settled here and gave shelter to travellers, and who later became a saint. The Rhine at this point runs narrow and deep, with strong currents, and passing ships needed local pilots. The river's nearby bend and the cliffs gave rise to the legend of the Loreley, just a short ride away. On the road, the B9 follows the west bank, with the railway line close by, and the corners are gentle and the views are wide. The ride up to Burg Rheinfels is a short, steep climb, with a few hairpins and a car park near the entrance. Take it slowly, because it is narrow and shared with walkers. The back roads into the Hunsrück hills are quiet and twisty, a good alternative if the river road is crowded.
With just over three thousand people, St. Goar has fuel and a handful of shops, but Boppard, about twelve kilometres north, has more choice. Restaurants along the riverfront serve Riesling and local dishes, and the terraces are pleasant on summer evenings, with ship traffic sliding past.
Come in spring or autumn to avoid the crowds, and enjoy the mist rising off the water.