The total distance of the 100 tallest buildings if put one atop one another is 30 km. What has more than 3 times that distance?

Grenville Gold's Pacococha Underground Workings: 98000 meters (or 98 km)!!

http://www.infoplease.com/ipa/A0001338.html

World's Tallest Buildings^: total 29953 meters or 30 km

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The Opportunity Show August 23, 2007
August 23, 2007 - Hosted By Troy Duran

Paul Gill, President: "The immense size of this, were coming to grips with it, we have 98 km of underground workings, that have been mapped so far, just imagine the size of this [...] there's a considerable amount of ore that's left there and god knows what's underneath it".

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http://www2.worksafebc.com/Publications/OHSRegulation/Part22.asp

"Underground working" includes any adit, tunnel, underground excavation, chamber, caisson, raise, shaft, winze or natural entry.