Biosphere 2 is a 3-acre (1.2-hectare) laboratory of glass domes in the Arizona Desert that houses five different ecosystems and was designed to be a prototype space colony.

In 1991, four men and four women were sealed inside this futuristic glass compound. The researchers, known as Biospherians, spent two years in the self-sustaining habitat, totally cut off from the outside world. The aim was to demonstrate how people might live in self-sufficient communities on the moon or Mars. Today, this large ecological experiment is a research center and tourist attraction.

Visitors are taken on a 1-mile (1.6-kilometer) route under the glass roof. Before stepping into this simulation of the Earth’s ecology, view the exhibits and multimedia displays in the visitor center. They chart the past, present and future of the project.

The tour starts in the human habitat where the researchers lived. See the kitchen and dining area and the farm where they grew their crops. Then pass through an airlock door into the wilderness areas.

Stand on the 40-foot (12-meter) cliff and look down at the 1-million-gallon (3,785,411-liter) ocean and its beach. Observe the rock forms and shrubs of the desert, modeled after coastal deserts along the Pacific Ocean. Step into the tropical rainforest containing more than 150 plant species. Look at some of the current research projects studying the effects of climate change.

The tour concludes in one of the two lungs, large geodesic domes that originally prevented Biosphere 2 from imploding or exploding. The machinery compensates for changes in air pressure caused by alternating day and night temperatures.

The mini world in the desert is open daily except Thanksgiving and Christmas Day. Tours depart every 30 to 45 minutes. They last for approximately 75 minutes and involve a lot of standing.

Biosphere 2 is located 36 miles (58 kilometers) to the north of Tucson and accessible by several highways. On-site car parking is free.