Renaissance fairs don’t really exist in Europe. Most countries have their own traditional festivals and customs which date back to that time period.
Castle Fest is centered around music (I think it was originally organized by the folk band Omnia), but has tons of combat and archery demonstrations, a market with clothes and weapons (blunt steel and boffer), esoteric stuff and anything else that vaguely fits in there.
Elfia, formerly known as the Elf Fantasy Fair is a fantasy-themed cosplay festival held twice a year.
Keltfest (10,000 visitors, apparently) is about ancient crafts, music, archery, with workshops and demonstrations.
I've also been to a few smaller ones I forgot the names of, but these are all pretty big, I think.
We have them in Slovenia. In the summer local castles will put on a fair for the tourists and kids. Sometimes multiple!
Typically you get a visiting troupe or two from Italy, they like to do flag twirling shows. There’s always a group of folks from Czech who put on an armored fighting competition. I’ve seen jousting tournaments too. And then you have a slew of local artisans selling wares roughly inspired by the time period. There’s often an outdoor play or two, maybe belly dancing.
It’s all great fun.
I went to all of them because I have young kids and they love that stuff. It's a fun day out. Also gives us an excuse to wear all of the arms and armor we've collected, lol.
There are lots of these in Austria, too, BTW. There was a two-week-long joust fair/festival by Millstätter See in early August!
In truth, these festivals are all over Europe. They're just not well advertised, so you have to look for them.
The next one in the region, by the way, is the medieval-themed Advent festival at the castle in Friesach. (Austria.) I'll be there for sure.
Considering how crowded they feel, I’d say the advertising is plenty sufficient. They’re local events with limited space.
Ah, anyway, it's nice that there's always something to do on a Summer's weekend...
Not sure how much they resemble American ren fairs, but they tend to have falconry exhibitions, smiths forging stuff, sellers of wooden toys and artisan jewelry..