Germany Commemorative Cancel

I acquired this block of four 3pf stamps depicting Adolf Hitler. It is overprinted with a cancelation or overprint that seems to depict some kind of event. What is this overprint/cancel commemorating? It has seven lines of text and shows a castle on a hill above a grove of trees. It reads, to the best of my ability, BAD LIEBENZELL (WURTT)/31 5. 44 17/Schmor3wald/Thermalond/Suftfurort/felt 1000/Jahren