I wish I'd had time to explore these ruins more thoroughly. Here is a shot from the far end of the courtyard one enters after passing through the Friederichsbau. There are a number of tower turrets around the castle in ruins like this. According to this webpage, for a time the castle was used as a quarry -- locals would take stones away to build new building in Heidelberg. This was stopped in 1800 by Count Charles de Graimberg who made every effort to preserve the Heidelberg Castle.

turret ruin