In the United States, the term mole people is sometimes used to describe homeless people living under large cities in abandoned subway, railroad, flood, sewage tunnels, and heating shafts.

Underground living refers to living below the ground's surface, whether in natural or manmade caves or structures. Underground dwellings are an alternative to above-ground dwellings for some home seekers, including those who are looking to minimize impact on the environment. Factories and office buildings can benefit from underground facilities for many of the same reasons as underground dwellings such as noise abatement, energy use, and security.