Quiet mid-week trip to Heidelberg focused on walking and being outside rather than sightseeing in the classic sense.
Philosophers Trail
The Philosophenweg lived up to its reputation. The views over the Neckar and the old town are excellent, especially in the late afternoon light. Not too crowded on a weekday.
River & Town
Spent a lot of time just walking along the Neckar and through the old town without a fixed plan. The combination of the river, the castle, and the surrounding hills makes Heidelberg feel very balanced. Good private visit.