Hummm … funny, I thought. This is one of those churches, that have at their heart not the usual naves and altars, but instead a house or, like in this case, a grave. It’s always something like “The House of the Virgin Mary” or “The Original Grave of Christ”, or something like that.
I can’t remember having seen this anywhere but in Italy. There, it is not exactly frequent, but it’s not unusual either.