"Found" doesn't mean it was "just found."

http://en.wikipedia.org/wiki/Derinkuyu_underground_city

"It was opened to visitors in 1969 and to date, about half of the underground city is accessible to tourists."

However there are new (big) areas discovered in 2014 -- referred to as "a new underground city:"

http://www.hurriyetdailynews.com/new-details-emerge-in-massi...

"The underground city was discovered by a Turkey’s Housing Development Administration (TOKİ) urban transformation project. Some 1,500 buildings located in and around the Nevşehir fortress were demolished, and the underground city was discovered when the earthmoving to construct new buildings had begun.

Hasan Ünver, mayor of Nevşehir, said they were going to meet with the TOKİ head and make a plan regarding the underground city. "