There was a good book about a recent discovery a few years ago, Lost City of the Monkey God. The locals had stories about some city in the jungle. The team managed to find it with LIDAR, but it was a slow, difficult process. They then had to land in fairly distant clearing and hike to the location. From there the team had trouble finding ruins even when they had their exact location, even once standing in right the middle of the city. The jungle hides a lot. The team members also came down with cutaneous leishmaniasis. Finding locations might be getting easier, but I imagine it would be difficult to find people with the right combination of skill and willingness to die a slow, agonizing, and disfiguring death to actually excavate some of them.