What belongs in the index
Our four main entries cover settlement and refuge, purpose-built tunnels, infrastructure in excavated architecture, and underground movement. They introduce comparisons rather than attempt a complete gazetteer. Derinkuyu and Montréal may both be described as underground cities, but the phrase conceals fundamental differences in date, function and physical form.
How sources are used
We link to heritage organisations, museums, public bodies and responsible operators where they provide a useful starting point. A UNESCO listing establishes a heritage context; it does not authenticate every claim repeated about a site. An operator is usually the best first source for current access, but a visitor page may not resolve an archaeological debate.
Where a number needs a qualification, we prefer the qualification to a dramatic headline. Depth needs a reference surface; population needs a method; a construction date needs an event. We do not publish a “deepest” or “oldest” ranking without a meaningful basis of comparison.
Images and identification
Detail photography supports observation of masonry, openings, water channels and hardware. Unless a caption names a location, an image is illustrative and is not evidence that the depicted feature belongs to the place discussed nearby. Photographs cannot replace measured surveys or a site-specific engineering assessment.
Independence and corrections
This website is not affiliated with UNESCO, the named museums, transport operators or heritage-site managers. References to those organisations identify sources, not endorsements. We do not offer tours, access permits or engineering services.
Readers can suggest corrections through the research-note composer. Please identify the page and claim, distinguish a factual correction from a different interpretation, and include a traceable source. Corrections can be considered without accepting unsupported access claims or publishing sensitive entry instructions.