To be clear, yes, we can see everything from Google Earth or other satellite imagery, but that doesn't mean we can explore it. GE can't see into forests, canyons and caves.
Has every mountain been scaled? Has every ocean depth been mapped? Has every jungle been navigated?
Basically, the question is, is there any part of our planet left to explore? To put your foot on a rock and shove a flag in the ground and name it whatever you please. What are the main areas left for exploration that someone might want to try and do. Clearly not every square foot of the Sahara has been navigated, but that's a bit harder than say, a North American forest.