Crowning a 375-metre-high hill east of the Old Town, the castle is an architectural mishmash, but most of it dates to the early 16th century when it was largely rebuilt after a devastating earthquake. It’s free to ramble around the castle grounds, but you’ll have to pay to enter the Watchtower, the Chapel of St George, to see the worthwhile Exhibition on Slovenian History, visit the new Puppet Theatre and take the Time Machine tour.
There are several ways to access the castle, with the easiest (and for kids, the most fun) being a 70m-long funicular that leaves from Old Town not far from the market on Vodnikov trg. There's also an hourly tourist train that departs from south of the Ljubljana Tourist Information Centre. There are three main walking routes: Študentovska ulica, which runs south from Ciril Metodov trg; steep Reber ulica from Stari trg; and Ulica na Grad from Gornji trg.
You can explore the castle's various attractions at your own pace, or join one of the highly recommended 90-minute Time Machine tours, led by costumed guides who walk you through six of the city’s most noteworthy periods, starting with Roman Emona.
The castle's 19th-century watchtower is located on the southwestern side of the castle courtyard. The climb to the top, via a double wrought-iron staircase (95 steps from the museum level) and a walk along the ramparts, is worth the effort for the views down into the Old Town and across the river to Center. Within the watchtower, there is a 12-minute video tour of Ljubljana and its history in several languages.
Situated below the watchtower down a small flight of stairs, the remarkable Chapel of St George (Kapela Sv Jurija) is one of the oldest surviving remnants of the castle, dating from 1489. It is covered in frescoes and the coats of arms of the Dukes of Carniola.
The Slovenian History Exhibition (Razstava Slovenska Zgodovina) is an interesting and well-presented interactive exhibition on Slovenian history through the ages, running from the very earliest Roman times, through the Middle Ages, the 19th century, WWI and WWII, and ending with socialist Yugoslavia and independence.
Also worth a look, the castle's latest attraction, the Museum of Puppetry (Lutkovni Muzej), explores the world of puppetry, from the manufacture of marionettes and glove puppets to the staging of the shows themselves. It's very interactive and lots of fun.
The Ljubljana Castle Information Centre can advise on tours and events that might be on during your visit.