Hainan Trip: How to See the Entire Island in One Day

I can never get enough of Hainan, the tropical island in China. I've been to Hainan three times so far this year. If you only have limited time, how do you get the most of it? This time, I took Hainan high speed railway, the world's first circular high-speed railway around an island, challenged to tour around the island in one day. I picked four cities that can represent Hainan the most, from east, west, south and north. Thank ‪@Eric_Garrison‬ for joining the epic-long day!