Okay kiddo, let's talk about charnel houses. Some people in the olden times used these places to store the bones of dead people. Imagine a big closet, like the one where we keep our clothes, but instead of clothes, it's filled with bones.
Charnel houses were usually located next to churches or graveyards, where people buried their loved ones. This is because sometimes the burial sites would get too crowded, so they would have to move the bones to a charnel house.
The bones would be sorted and stacked in the charnel house, and sometimes they would be arranged in cool patterns or designs. People would sometimes visit the charnel house to pay their respects to the dead, or to just look at the creepy bones.
Nowadays, we don't really use charnel houses anymore, as we have better ways to dispose of and honor the dead. But back then, it was a way to, in a strange way, keep the memory of the deceased alive.