What makes this place so cool and creepy is all of the ossuary's bones are on display in a decorative fashion. Tens of thousands of people's bones piled into pyramids, arranged into a shield, and then the famous chandelier which has at least one of every single bone in your body.
There's an interesting history to it, and you can read more here:
We took the night tour which is only narrated in Czech, and is naturally creepier after dark. Even though we didn't understand a single word of what the guide said, mostly we wandered around inside and took creepy pictures for the hour. Lighting was really difficult because the whole place was only lit by candlelight, but with some camera adjustments, we were able to get some pretty good shots. And a couple on our phones, which I can share with you here.
After the main tour, the monk guy took us outside (through the graveyard for a minute) and upstairs, where we got a special performance of one monk singing, another one playing the organ, and the original guide controlling the airflow of the organ, I think. This took up almost another hour, and it was super cool because one of the monks looked like a knight from Lord of the Rings , and he sang really loudly, I actually jumped.
This is us before, getting excited for our "night out." Forget the pub crawls and partying, we're going to a Czech Ossuary, dude!
(Since we each hate ourselves in the opposite picture, the compromise is to post both.)