Dyson sphere
A Dyson Sphere is a colossal spherical structure constructed around a star, completely surrounding it.
The interior of the sphere would absorb the entire energy output of that star, allowing for lifeforms to live on the interior surface almost indefinitely.
For the interior of a Dyson Sphere to be habitable to most humanoid lifeforms, the radius of the sphere must be such that habitable temperatures (5 – 30 °C) are maintained. The radius would therefore depend on the size and the energy output of the star around which the sphere would be constructed; if a Dyson Sphere were to be constructed around the Terran sun, the radius would have to be approximately one astronomical unit. At such a radius, the interior surface area would be about 7 × 1016 km2, or 550 million times the entire surface area of the planet Earth. Such a surface area could easily support the lives of many quadrillions of beings.
Due to the almost immeasurable amounts of effort, resources, and time required to construct this immense structure, only one Dyson Sphere has ever been discovered. This particular sphere encased a G-type (yellow) star, and had a diameter of 200 million kilometers. This give it an internal surface area of approximately 250 million M-class planets. As no radiant sunlight or solar wind escaped from the sphere, starships were not able to detect it until they were almost on top of it. As a result, the USS Jenolan crashed onto it in 2294 after being pulled in by the sphere's immense gravity well. In 2369, the Enterprise D discovered the Jenolan and investigated the sphere. The sphere was deserted because the star around which it was constructed was highly unstable.
