What is sacred ground?

Each week I go out for breakfast with my son, usually at Hungry Jack's. We read the newspaper and talk about a Christian book we are reading.
This is one of the few times in the week when I look at a hard copy of a newspaper. I still prefer it to reading online.
In today's Australian newspaper there is a good column by Greg Sheridan, Both sides guilty of excess in US Islam debate.
He mentions an excellent column by Charles Krauthammer, Sacrilege at Ground Zero, which gives a persuasive and balanced argument about why building a mosque near the site of the 9/11 attacks is not a good idea. He points out the relevant example of how Pope John Paul II ordered Carmelite nuns to leave the monastery they had build near Auschwitz because it was an inappropriate location.