This is a must-do activity when you visit Krakow. The Castle dominates the city and is a beautiful experience walking through the grounds. Everyone who goes to Krakow visits the Castle. The problem is that the city knows this and there are monetary micro-transactions everywhere to see different elements of the castle itself (e.g., royal garden, dragon den). Moreover, there are tonnes of tourists and huge queues to get a guided tour at the ticket office.
My advice ... don't get a guided tour. Just walk around the grounds. Some people think they need to go to the ticket office to pay for admission, but admission to the grounds is actually free. The office is only for guided tours. So, you often see people queuing for ages for no reason thinking that is the only way to see the Castle.
The grounds are lovely, free, and enough of an experience to get a sense of Wawel.