Lightning struck Heidelberg Castle in 1764 and the Krautturm was never rebuilt; its split shell still hangs open above the valley. Below the ruin, the Altstadt runs roughly 1.6 kilometres along the south bank of the Neckar, its Hauptstrasse counted among the longest pedestrian streets in Europe. The quarter charges nothing to enter — 0 EUR — because Altstadt, 69117 Heidelberg is a working district rather than a gated monument. Heidelberg and Rothenburg Day Trip from Frankfurt tours bind this quarter to a second walled centre 180 kilometres east. What stands here is younger than it looks. French troops burned the town in 1689 and again in 1693, and the reconstruction that followed set Baroque facades onto a medieval street plan — uniform frontages, crooked alleys. The Alte Brücke, finished in 1788 under Elector Karl Theodor, was the ninth crossing raised on that spot; the eight before it went to ice and flood. Heiliggeistkirche took the market square from 1398 onward, its roof lifting above merchants' stalls that still trade beneath the buttresses. The university, chartered in 1386, remains the oldest in Germany, and its students left the town two of its odder monuments: the Studentenkarzer and the castle's Großes Fass, a wine barrel of some 220,000 litres. Rothenburg ob der Tauber survived by a different accident. Trade routes and railways bypassed it after the Thirty Years' War, and poverty preserved what prosperity would have demolished. Its ring wall runs about 3.4 kilometres, with a covered sentry walk of roughly 2.5 kilometres and more than 40 towers and gates. Air raids in March 1945 destroyed a substantial share of the eastern old town; donors from abroad paid for the rebuilding metre by metre, and their names are cut into the wall walk still. The Plönlein — a fork of lanes beneath two gate towers — became the most reproduced corner in Germany. The two towns anchor opposite ends of a single southern German idea: the fortified centre kept intact. Heidelberg Old Town walking tour routes read that idea in Baroque; the Romantic Road landmarks strung north of the Tauber read it in half-timber and stone. A Heidelberg and Rothenburg Day Trip from Frankfurt tour holds both in view — castle terrace above the Neckar, rampart above the Tauber — and lets the contrast do the argument.