Café Knösel on Haspelgasse, just off the Hauptstrasse, claims to be Heidelberg's oldest café and has been serving coffee and cakes in the old town since the 1860s. It has the deep, slightly faded interior of a Central European café — dark wood, framed prints, and the smell of roasting coffee — and is popular with an older clientele and visiting academics alongside the usual mix of tourists.
Knösel is famous across Germany as the birthplace of the Heidelberger Studentenkuss — the Heidelberg Student Kiss — a chocolate praline filled with nougat and marzipan, created here in 1863. The story attached to it is that the chocolates were developed as a way for young men to pass a sweet message to women in the café without violating the strict rules governing contact between the sexes in Wilhelmine Germany; the chocolates could be offered and accepted without impropriety. Whether the story is entirely true is uncertain, but the chocolates are still made to the original recipe and sold here and in shops across the city. They make a good souvenir.
The café serves full breakfasts, light lunches, and an extensive cake selection in the afternoon. It is open daily and is a good choice for a quiet coffee away from the bustle of the Hauptstrasse.