Three days in Heidelberg: a castle nobody rebuilt, above a university older than the country

Start at the market square, halfway along the old town, with the Heiliggeistkirche on it. The church was built between 1398 and 1515 and once held the Bibliotheca Palatina, the greatest library in Germany, which was carried off to Rome as war booty in 1622 and has only ever come back in pieces. For centuries a wall ran down the middle of the nave so that Catholics and Protestants could use it at the same time without meeting.

The main street runs the length of the town from here, closed to cars the whole way, and is said to be the longest pedestrian shopping street in Germany. Walk it in either direction, look into the courtyards, and note that Heidelberg came through the last war almost untouched, so the buildings are the real thing rather than reconstructions.

Then go down to the bridge for the evening. The Karl Theodor bridge was built in sandstone in 1788, blown up by retreating German troops in 1945 and rebuilt by the town within three years. At the old town end there is a monkey cast in bronze with a mirror in its hand, a joke about vanity that has been on this crossing in one form or another since the fifteenth century, and the view from the middle of the span is the one on every postcard of Germany.

Go up early. The castle is red sandstone on a terrace above the town, and what you walk through is the wreck of four centuries of building: the Renaissance palace fronts with their rows of statues, a courtyard, a blown-out tower lying on its side where the French demolition charges dropped it in 1693, and gardens with a view straight down the valley. Lightning finished the job in 1764 and the ruin was left alone, mostly because the romantics arrived and decided it was better this way.

Two things inside are worth finding. The Great Tun is a wine barrel the size of a room, built in 1751 to hold the tax paid in wine by the surrounding villages, with a dance floor on top of it. The pharmacy museum next door is far better than it sounds, being several complete apothecary shops from the sixteenth century onwards moved here and reassembled.

The funicular carries on above the castle to the top of the mountain, 568 metres up, in wooden cars a century old. The view takes in the Rhine plain and, on a clear day, the northern edge of the Black Forest. Come down, cross the river and walk the Philosophenweg on the north bank in the late afternoon: a steep lane through vineyards and gardens that professors have walked for two hundred years, and the place the town is drawn from.

Heidelberg's university was founded in 1386, which makes it the oldest in Germany and older than the country it is in by five centuries. The old university building stands on its own square two streets from the market, and the museum inside covers the whole run of it, including the Great Hall and the period when the university was one of the first to fall in behind National Socialism.

Round the back is the reason most people come: the student prison, in use from the late eighteenth century until 1914, where undergraduates were locked up for a few days for drunkenness, duelling or letting pigs loose. They treated it as a badge of honour, brought food and beer in, and covered every wall and ceiling with portraits, poems and the dates of their sentences. It is all still there.

If there is time before the train, the city museum on the way back towards the bridge holds the local painting and a fifteenth century carved altarpiece, and it is quiet. Otherwise the bus from Bismarckplatz reaches the station in ten minutes.