From c.21 mins:
https://www.bbc.co.uk/iplayer/episode/b06h3ytf/the-celts-blood-iron-and-sacrifice-with-alice-roberts-and-neil-oliver-episode-1

Been to Hallstatt many times its a wonderful place , stay just outside at Obertraun its where a cave dive called " Die Kessel " starts , now that is a very serious undertaking  There is also the very unique and quite bizarre place called " Die Beinhaus" 

https://www.hallstatt.net/ueber-hallstatt/sehenswertes/katholische-pfarrkirche-hallstatt/beinhaus-hallstatt/