This is Grad Snežnik (Snežnik Castle) near the village of Kozarišče, about 28 km from Lake Cerknica, Europe’s largest intermittent lake, in south central Slovenia. It’s tucked nicely into the southwest corner of the Lož Valley, on the edge of hundreds of square kilometers of beautiful forests and rough forest service roads where one can —and where I have, on several occasions!— get pleasantly lost.
It’s said to date back to the 13th century and was likely built on a site where a Roman stronghold once stood. It was fully renovated in 2008 and is the only castle in Slovenia with surviving authentic interiors.
It’s far enough away from main highways and train stations —truly off the beaten path— that it’s not very heavily visited. I’ve been here many times, in all seasons, weekdays and weekends, and besides one wedding that I nearly crashed, I never shared the castle with more than half a dozen people.
A little more is here on the national museum website.