What's the fastest, easiest and cheapest way to go to Beijing World Park?

1. Do you refer to City Inn Happy Valley Beijing? If yes, from your hotel, walk east around 550 yards to get to Happy Valley Scenic Area Station. Take metro line 7 to West Railway Station and metro line 9 to Guogongzhuang Station. Then transfer to metro Fangshan Line to Dabaotai Station, Exit B. After arriving, walk to the destination directly.
2. Generally speaking, you can still see the cherry blossom until the early May. Thus I'm afraid that you may not see it in the mid/end of May. If possible, you'd better to change the travel plan.