My flat is in the very center of Heidelberg in the "Altstadt" (Oldtown). You literally can't be more central - it's just 3 walking minutes from the Bismarck Square, the focal point of Heidelberg.
I rent the ca. 60m² flat this winter for several weeks, ideal for an extended business trip stay (University, SAP, EMBL...)
The flat is fully furnished with a complete equipped kitchen diner, living room with sofas and big desk, sleeping room, bathroom and storeroom.