Founded in 1904 and run by the University of Hawai'i at Manoa since 1919, the Waikiki Aquarium is the second-oldest public aquarium in the United States and sits directly across the road from a living coral reef. Compact but exceptionally curated, its 3,500 organisms across 490 species focus on Hawaiian and Indo-Pacific marine life, including a glowing cylinder of moon jellies, the only chambered nautilus bred in captivity in the US, reef sharks, a giant clam exhibit, and a rescued Hawaiian monk seal in a large outdoor enclosure. Expect to spend 60 to 90 minutes and pair the visit with a walk through neighboring Kapi'olani Park. Audio guides are included; admission is $12 adults, $5 kids. Time your visit for the 11 a.m. or 2 p.m. monk seal feeding.
"The jellyfish tank is mesmerizing and the outdoor monk seal area was a huge hit with our kids. It is small but every exhibit is thoughtfully done, you can see real conservation work happening."