When I go to yoga it is a "sacred place" because people are very respectful and and the atmosphere is relaxing.  The people that attend the yoga classes are very respectful of everyone else.  Everybody leaves their phones out of the room to keep the place quiet.  Also the room being quiet is nice because it helps you relax and clear out your thoughts.  I think the most important is how the instructor runs it because they are going to set the tone of the whole lesson.