Hierarchy classification:

1. top of the aat hierarchies
2. Objects Facet
3. Built Environment (hierarchy name)
4. Settlements and Landscapes (hierarchy name)
5. landscapes (environments)
6. natural landscapes
7. landforms (terrestrial)

Narrower term/s

• natural tunnels

Anotations

Scope note:

Natural openings in the earth large enough for human exploration, the largest and most common being those formed by a chemical reaction between circulating groundwater and limestone or dolomite bedrock.