I’m going to Prague myself this summer and definitely visiting the Ossuary.
Awesome! Make sure you set aside a day to see it (if possible). It takes time to get there on the train from Prague and then to familiarize yourself with where the church is in the town. Luckily walking from the Kutna Hora train station to the church is only like 10 minutes. There’s a lot of detail to take in and for me at least, I found it to be a really beautiful and almost peaceful place (but I’m morbid haha). Have fun! :)