The Moscow Metro in Russia carries 8-9 million passengers each day. By comparison, the New york City Subway, USA carries 4.5 million people each day and the London underground , UK, carries just over 3 million.
The hottest layer of the Earth is its innermost layer. The inner core Quite literally the center of the Earth, the inner core is solid and can get to estimate temperatures over 9,000 degrees Fahrenheit