This is one of the main attractions in Prague. There are few different sets of tickets that you have to purchase to enter few buildings inside the castle. The St. Vitus cathedral is one of them, which is a huge and beautiful church. You can enter inside the church without ticket up to a limited area. Beyond that point, you will need to scan tickets. But I think, the visit without ticket would have been enough for me. The view of the beautiful city from the balcony was very impressive to me. The Golden Lane also needs ticket, but this area is very narrow and hence a bit crowded.
To me the ticket seemed a bit overpriced and one can get well inside the castle without ticket except the Golden Lane and few buildings which were not so interesting.
I bet that's a beautiful cathedral. Have you seen the one in Cologne, Germany? It's very similar.