From Destinypedia, the Destiny wiki
Site 6 (known also as the SIVA Replication Complex) is a location in the Plaguelands. It is an underground Golden Age complex that features SIVA's replication chamber, and is the source of the techno-plague abused by the Devil Splicers.
Site-6 was the location for the final stages of the Battle of Site-6 fought between Rasputin and the Iron Lords.
The SIVA Replication Chamber located here was later destroyed by The Guardian during the course of the SIVA Crisis