My girlfriend and I visited the Old Jewish Cemetery in Prague last year through a combined ticket for the Jewish quarter. Located next to the Pinkas synagogue, it's the second oldest Jewish cemetery in Europe after the one in Worms. There are a total of roughly 12,000 gravestones layered on top of each other, the oldest one dating as far back as 1439. A particularly interesting feature of the cemetery is the depiction of foxes, lions, bears, axes, and other animals and objects on the tombstones - these images indicate the occupation or origins of the deceased. The animals and objects are portrayed because the Jewish religion does not allow pictorial depictions of the dead.
We got the tickets for the Jewish quarter through the Prague Visitor Pass and we also took advantage of the audio guides, which gave us some interesting information about the synagogue and the cemetery. Although for me personally this wasn't one of the top sights in Prague, I would still recommend it to anyone interested in history, Judaism or cemeteries.