The Mukai-yama (向山) complex in the southern portion of the island and the Achiyama lava dome at the northern end were formed during Nii-jima's only historical eruptions in the 9th century AD.

The Atchiyama rhyolitic lava dome and neighboring Wakago basaltic pyroclastic deposit contain rare xenoliths composed of gabbro.

However, the often repeated legend that Nii-jima and Shikine-jima were once a single island that was separated by huge tsunami caused by the 1703 Genroku earthquake has no basis in geology.

Even though Nii-jima is located relatively close to Honshu, the small population and lower exploitation has allowed the island's natural wildlife to be well preserved, and many varieties can be seen.

Riding on the Kuroshio current, many oceanic species and birds migrate thorough the island, Indo-Pacific bottlenose dolphins that have seemingly moved to here, and other areas, from Mikurajima inhabit the near shores; along with nesting sea turtles, and the occasional visiting manta ray.

Almost completely wiped out, due to past hunting, biodiversity of other marine mammals, such as cetaceans and pinnipeds, have become very small and today are only a remnant of their historical numbers.

[7][8] Additionally the, possibly now-extinct, Japanese sea lion used to breed in the Izu Islands and in the vicinity of Nii-jima, there was a colony on Udone-shima.

[9] Nii-jima is 2 hours and 20 minutes away by jet boat from Takeshiba Sanbashi Pier, in Tokyo, operated by Tōkai Kisen.

Nii-jima has been inhabited since prehistoric times, and archaeologists have found numerous remains from the Jōmon period, including stone and ceramic utensils.

Habushi Beach, on the eastern side of the island, is a nationally protected reserve with its waves and white sand, and is a good location for surfing.

Jūsansha Jinja, is a Shinto shrine at the base of the cliffs of Mount Miyatsuka in the north-western corner of the main village on the island.

This shrine, built in the Edo period, is recognized as caretakers of intangible cultural assets by the Tokyo government for the kagura music and sacred dancing, known as shishi-kiyari that are held every December 8.

The cemetery, covered with the local white sand, is dominated by the gravestones of the 118 exiles, banished to Niijima by the Tokugawa Shogunate during the Edo era for non-political crimes.

A collaborative effort between the education board and the English department at Niijima High School ensured that the museum is completely bilingual: Japanese-English.

Souvenirs from Niijima include the island specialty kusaya - a dried fish, usually mackerel scad (Decapterus macarellus), that has been soaked in a special brine.

Other souvenirs are milk senbei, the ashitaba plant, Niijima glass art, and a local Shōchū called Shima Jiman, island pride.