DNA, because the Blue Mountains have much less pollution than the city and it is filled with millions of trees that absorb Carbon Dioxide, the oxygen is more pure than the city. But of course it wouldn't have 100% oxygen since there is some other chemicals in the atmosphere. Oh yes, and the opal is really hard to find. They probably sell it there after mining in the past. The opal is only found in the East Coast of Australia and a few parts of Mexico. The train track is actually vertical, but the seats are bent 52 degrees. Thank you for asking! I tend to read a lot and memorise the information!