With kids, it depends on the day.
Time your pass through Luža Square for the top of the hour and you catch the Zelenci — two bronze 'green men' who have swung their hammers at the bell since the 16th century (the originals are now indoors, replicas do the public striking). It's a 30-second piece of living clockwork that locals still set their step by. The honest catch is that off the hour it's a look-up-and-admire landmark you can't enter or climb; it earns its place as a timed micro-moment, not a ticketed visit.