http://en.wikipedia.org/wiki/Derinkuyu_Underground_City
*Note: This is all underground.
"The complex has a total 11 floors, though many floors have not been excavated. Each floor could be closed off separately.
The city could accommodate between 35,000 and 50,000 people and had all the usual amenities found in other underground complexes across Cappadocia, such as wine and oil presses, stables, cellars, storage rooms, refectories, and chapels."
How a population manages to maintain itself underground with the risk of collapse, disease, sanitation issues etc. is way beyond me. Seems a bit surreal.