Try Beidaihe (beach) or Badailing Great Wall area (mountain) resorts, both within 2 to 3 hours of driving or train distance, or go further north to China's oil capital, Daqing City in Heilongjiang (average temperature is about 25 degrees in the summer) by flight (about 2 hours)

Another option is taking a train to Chengde. This was one of the summer retreats of the Emporer Kangxi and as you can guess, the main attraction there is a palace, temples and numerous pagados, similar to the Forbidden City in Beijing.

Trains leave from Beijing Railway Station and the whole journey takes 4 hours. Once you get to Chengde, just take a cab to the summer palace. Staying there for a night is highly recommended though if you don't want to rush.

Water cube ( Beijing National Aquatics Center) on the 4th north ring (Olympic park) has a water amusement park. Full of fun and it's great for family, kids, and friends get together. No matter how old you are, you will enjoy the water fun and water slide adventure.