Why did Sauron station himself at Dol Guldur, why not somewhere more isolated?

Would it not have been better for Sauron to go to somewhere more isolated where he could build up his strength in even more secrecy, say somewhere like Rhun or Khand.

Dol Guldur whilst somewhat isolated in Mirkwood was still quite close to the two Elven realms. He must have realised that it wouldn't be too long before people noticed something strange was going on at the old fort.

I've seen some people say he chose Dol Guldur because it was close to the Gladden fields and wanted to search for the ring but correct me if im wrong but at this point in time Sauron believed the Ring had been destroyed.