Falkovnian Central Prison

[Jester of the FoS]

Well, given the number of first-hand reports, wood carvings and stories about Vlas Tepes impaling his prisoners I am very doubtful they are just a legend. It is unlikely they were vast forests of the dead and he probably didn't eat amongst said spikes, those sound like local exaggerations, it was still a punishment he used from time to time.
However, like crucifiction, impalement was a common and widespread punishment. It was en vogue at the time and Vlad was in no way the only king to do so. He's just the most famous.