If you like your travel experiences to involve death and the reminder of mortality, then the top of your list should be the Sedlec Ossuary in Kutna Hora, just outside of Prague in the Czech Republic.
I went for my birthday and the irony of spending the day of my birth in a place filled with thousands or corpses was not lost on me. In fact it was a nice reminder of the temporality of life, and that there can still be beauty in death even after the flesh has melted from our bones.
The Sedlec Ossuary is said to contain a small amount of earth from Golgotha that the abbot from the Cistercian monastery brought back from the holy land in the late 13th Century. When news of this spread, the (then) cemetery became a very popular burial ground among people. Of course use of the cemetery only grew after the black death in the mid 14th Century.
A chapel was built in the middle of the cemetery with a lower level to house the bones exhumed from the site. The beautiful and macabre result of the arranged bones that we see today did not happen until 1870 when František Rint, a woodcarver was employed to arrange the piles of osseous matter.
Well worth the travel, this place is at the top of my list so far for intrigue, fascination and morbidity.