Great visit— here is some practical information:
We visited Saturday September 23, 2023. There were no lines at security as they were not checking bags— we just walked through past a policeman. This was true at both the main entrance and the entrance near Lobkowicz Palace.
At 9:45 AM at the Information Centre in the 3rd Courtyard, there was no line at all for tickets or audio guides or to pay for the group tour— so no need to buy tickets ahead of time (but you must reserve the group tour ahead of time— email them a week or more before you go). In fact, we regretted buying tickets ahead of time through Lobkowicz Palace, since that meant we had to pick up the tickets in person at Lobkowicz Palace, which did not open until 10:00 AM, and there was a fifteen minute line there! (And you can’t buy the audio guide without showing your ticket!).
The audio guide is very good, and gives you info on more than what is covered by the group tour (which covers the Cathedral and Old Royal Palace), so if you want the full experience get both. In fact our tour guide made a point of us not using our tickets to get into the Cathedral (tickets can only be used for one entry), so that we could come back later to look more on our own, which was great.
Lobkowicz Palace was excellent, with a great included audio guide— if you love history, don’t miss it! It may be a little quieter than the rest of the site, so maybe save it for the busiest part of the day. And be sure to spend time on the terrace at Lobkowicz Palace, enjoying the incredible view!
Golden Lane was ridiculously crowded in the middle of the day, a bit commercialized, and not too special (though I did enjoy the tiny torture chamber and dungeon 😀), so don’t worry if you miss it. There are several nice places to eat, including a cafe with a great view of the Cathedral.