Strip the supernatural aspect out and just call it “important to the local culture”.

That's pretty much exactly what "sacred" means, yes. For the average westerner, religious or not, the term "sacred" smells of holy water created by someone in a fancy dress mumbling and waving their hands while for others it simple means "place of significance that should be honoured". These kinds of terms don't easily translate between cultural barriers even if everyone is, on the face of it, speaking the same language, see also e.g. the Native American use of the word "medicine".

Metalheads call the site of the Wacken Open Air festival "Holy Ground", and they have all the right in the world to do it. On the part of the people of Wacken you can be sure that they won't build anything on it, it's gonna stay a pasture -- a very well maintained one, the water management system is extensive to make sure rainfalls during the festivals won't turn it into a mudpit. Maybe, in case the villages around it grow together more, make some pathways through it and plant trees along the paths, but they certainly won't put a mall there. The vast majority of Wackeners, even if they don't partake in the religion of metal, don't mind a bit selling beer to the pilgrims so the site gets respected, just as the metalheads respect the site: They're cleaning it up perfectly each and every year. Right now it might seem a bit mundane, it's thinkable (if Wackeners weren't Wackeners) that someone would put a mall there, but give it 100 years of continued yearly ritual use and it'll become unthinkable.