It's going to get cheaper to go under the sea. Atlantis Submarines, which operates underwater tours off three islands, celebrates its 20th anniversary with special kama'aina fares for its sub journeys and dinner cruises.

Atlantis will continue to offer Hawai'i residents the special rate of $20 for adults and $10 for children (ages 12 and younger) for its submarine tours off Waikiki, Lahaina and Kona through the end of September — savings of up to more than 60 percent off regular fees.

From Oct. 1 through Dec. 31, kama'aina rates will be $37.70 adults and $16.16 children for the standard sub tour, and $49.55 and $33.39 for a premium sub tour.

Hawai'i residents also can save 20 percent off the regular price for Atlantis Cruises' sunset dinner cruises and more than 40 percent for a combination submarine and dinner cruise package through Dec. 31.

"We want to say mahalo to the people of Hawai'i for 20 years of support in helping to make Atlantis Submarines a world-class tour experience for enjoying the beauty of our marine environment," said Ronald Williams, president and CEO of Atlantis Submarines.

Atlantis launched its first sub dive site off Kona in 1988, and three years later, added dive sites off Waikiki and Lahaina. Guests descend to depths of 125 feet aboard the world's most technologically advanced passenger submarine in an air-conditioned cabin with personal viewing portals for watching marine life. In Honolulu, sub cruises depart from a pier near the Hilton Hawaiian Village.

Atlantis Cruises depart at 5:15 p.m. from Aloha Tower Marketplace for a two-hour sunset cruise aboard a 140-foot vessel, Navatek I, which accommodates more than 300 guests and features outdoor upper and lower observation decks, and two air-conditioned dining rooms with large picture windows. There also is entertainment aboard, plus from-the-sea vistas of Diamond Head and the Waikiki landscape. www.atlantissubmarines.com, 800-548-6262.

— Wayne Harada

MUSEUM DAY SEPT. 27

8 O'AHU MUSEUMS OFFERING FREE ADMISSION WITH SMITHSONIAN PASS

Eight O'ahu museums will offer free admission to Smithsonian magazine readers and those who visit Smithsonian.com during the publication's fourth annual Museum Day, Sept. 27.

The museums are: Hawai'i State Art Museum, Manoa Heritage Center, Mission Houses Museum, Pacific Aviation Museum, Queen Emma Summer Palace, University of Hawai'i Art Gallery, Bishop Museum and the Hawai'i Maritime Center. Close to 900 museums across the nation will participate in the Smithsonian Institution's celebration of culture, learning and knowledge.

To participate, you'll need a Museum Day admission card now available in the September issue of Smithsonian magazine, with a downloadable version available at www.smithsonian.com/museumday. Each card provides museum access to two people; one admission card allowed per household.