It's to cold so no one has visited Neptune. It's to far from the sun.
voyager 2
Only one through 2009. The Voyager 2 probe visited Neptune in 1989, having previously passed Jupiter, Saturn, and Uranus. Voyager 2 took the first close-up photos of the Neptunian moon Triton and...
So far only voyager II has visited Neptune.
1 time