You can pray anywhere you like, but there are some places that are more sacred than others, because either a holy being has lived there for some time and their presence has left an atmosphere that continues for ages and which would be worn out if it weren't for the people that come there and pilgrimage, and who strengthen the atmosphere of that place, like a djiner for example. As I talked about the other day, there are some places that are holy spots, meccas, because there was, one day, a being, in the case of Mecca it was Abraham, who prayed there or made a wish there and the heavens were moved by his prayer and the angels came, descended upon that place. That place is protected by the angels, and whatever one builds there, it won't take away anything except that, of course, it wears down a little bit in time unless people are able to come there and maintain their prayers at that place.