One thing amazing about these bricks which are actually made out of salt is that when you pass light through them each brick is distinguishable from the other. Also learnt that these structures houses patients of asthma. Some research has proven that the environment has a great effect on Asthma patients.
Khewra Salt mines is the world's second largest salt tunnel system, after one in Argentina. more: en.wikipedia.org/wiki/Khewra