The War Memorial Natatorium was originally built in 1927 to remember those who fought and served in World War I. It is a (now closed) saltwater swimming pool built right off the beach and into the Pacific Ocean.
The Duke Kahanamoku, renowned Hawaiian surfer and Olympic Gold Medal swimmer, took the first swim at the Natatorium.
Kaimana Beach is a great place to visit along with the Memorial. The sand between Diamond Head and Kapiolani Park is a beautiful place to to throw down a beach towel and enjoy the beautiful water right next to the memorial (and just far enough away from the busy stretch of Waikiki Beach).
More recently, the war memorial has been closed due to problems with its structural integrity. There was an ongoing dispute as to whether the memorial should be torn down or restored. In May 2014, the National Trust for Historic Preservation named the War Memorial Natatorium a National Treasure. Perhaps the pool will open again.