Kutna Hora is a small city located an hour from Prague by train. Trains run everyday back and forth from Prague main train station to Kutna Hora, return for less than £10.
The city itself has become a UNESCO World Heritage site. But it’s best known for it’s bone chapel, the Sedlec Ossuary, which is located 10 minutes from the city centre. The chapel is reasonable priced, for students it’s only 70 crowns entry, including a ticket to see another cathedral nearby (that’s only £2.30 for 2 entrances!). But it’s very creepy.