They used Cesky Bud previously - the huge main square made for an impressive display.
Lipno will probably be a better 'Fest' destination though & nearby Cesky Krumlov is a lovely old Bohemian town, well worth a detour.
However I really can't be asked, when it comes to actually attending a rider fest. OK, we found ourselves around 30 miles from Faak when there was an HD meet once, which meant there were plenty of Harley riders around wherever we went in the area, but that is as close as it gets for me. I'm far too old & grumpy.
Naturally, it's each to their own - give it a try if it floats your boat.