Fort Condor is a solitary reactor that stands by itself out in the middle of a rocky field and on the side of a cliff. It can be found in the southeast section of the eastern continent just southeast of Junon.
Fort Condor is the location for an optional side quest that you can partake in. You can find additional details about the side quest in the Fort Condor side quest section. That being said, there is a part of the game where you are forced to participate in the mini-game here. Check out the Fort Condor walkthrough page for more details.
There are some items that you can purchase in this location. These items change after Meteor has been summoned and after Tifa has been rescued from Junon during the second visit.
The map below shows the location of the Fort Condor on the World Map: