CHONGQING, Sept. 27 (Xinhua) — An underground nuclear plant in southwest China's Chongqing Municipality has officially opened to the public as a tourist site, local authorities said Tuesday.

Located in a mountainous area in Fuling district, the 816 nuclear facility, covering an area of 104,000 square meters and stretching for over 20 kilometers, is believed to be the world's largest artificial cave, said the district tourist bureau.

It has 18 large main caves and more than 130 roads, branch caves, tunnels and vertical shafts.

Construction on the project started in 1966, but the country called it off in 1984 due to a favorable international environment. More than 60,000 workers helped with construction.

The plant was intended for nuclear reaction but never put to military use. It was turned into a factory manufacturing chemical products in the 1980s.

The plant was declassified in 2002.

With an investment of 60 million yuan (9 million U. S. dollars), the plant underwent a facelift adding safety and tourism facilities in 2015.

Tickets for the site are 60 yuan per person in peak season, April to October, and 45 yuan in off-season, November to March.