The waters around the Poor Knights have been described as ''dive heaven''.
The islands and surrounding waters have worn the ''marine reserve'' title since 1981 but have only been fully protected since 1998. That year, the Poor Knights Islands Marine Reserve status was bolstered to include a total fishing ban.
Experienced and novice divers from all over the world are drawn to the Knights' famed underwater scenery - its cathedral-type arches, caves, cliff faces, sponge gardens and kelp forests, clear water, and the sea life.
Above water, the predator-free islands are a unique environment, rich with birdlife and some endemic wildlife and plants. Only people with special permits, such as scientists and Department of Conservation (DoC) staff, are allowed to set foot on the rugged, cliff-fringed islands.
Last month's 20th anniversary of the marine reserve passed fairly quietly. Today 48 Hours is celebrating the event with 20 facts provided by DoC and excursion company Dive! Tutukaka. Photos from the Northern Advocate's archives and courtesy of several contributors.
1. There are two large islands and over 24 islets and rocky outcrops. The land and the sea extending for 800 metres around the islands is a marine reserve.
2. Around 25,000 people visit the reserve annually.
3. There are more than 120 species of sealife, with new ones being discovered each year.
4. Why Captain Cook bestowed the islands' name in November 1769 is not clear. Some say the outline on the horizon resembled an effigy of a knight lying down or a poor knight's pudding, a bread-based dish popular at the time.
5. Jacques Cousteau ranked the Poor Knights as one of the top 10 dive sites in the world.
6. It was declared tapu by local Māori after a bloody massacre around 1820.
7 More than 400 people once lived on the islands with five known pa sites, marae, and terraced gardens.
8. Locals call it the Cetacean Highway as it's on the migratory path of common and bottlenose dolphins, and orca, humpback, blue, sperm minke, Bryde's and pilot whales.
9. The largest sea cave in the world by volume is Rikoriko Cave.
10. A dead sperm whale washed up inside Rikoriko, making it almost impossible to go inside due to the smell as the skeleton rotted and sank.
11. In World War II a Japanese submarine hid inside the cave for two weeks while undergoing repairs.
12. In Māori Rikoriko means waning light, twilight, or dancing light - referring to the sunlight patterns reflected off the water surface onto the cave walls and ceiling.
13. Rikoriko is renowned for its acoustics. When the band Herbs played in the cave, Wade Doak submerged audio mics transmitting the live sound, and dolphins entered the cave and swam to the music. Neil Finn performed in this natural auditorium. Impromptu performances include Gregorian chants, Māori haka, opera singers, Swiss yodellers, Irish folk singers and didgeridoo players.
14. The islands are the only nesting place in the world for Buller's shearwaters.
15. They are home to more than 1000 tuatara, many of which share the burrows of shearwaters.
16. There were no land-based mammals until introduced by humans. The islands are now pest-free.
17. The world's largest insect, the giant weta, is endemic to the Poor Knights.
18. The large Poor Knights lily is endemic and is flowering now (spring).
19. The islands' plants have gigantism, where they are larger than their mainland counterparts.
20. Every experience is different at the Poor Knights Marine Reserve and just when you think you've seen it all, you see something new and exciting.