Martian dawn. Photo taken August 13, 1977 by the Viking 1 Lander. Pruned
Even though it was unarguably impressive to get people to fly to the moon — and back!, the feat of space exploration that impresses me most is the Soviets getting the Venera spacecrafts to land in fucking Venus and transmit pictures just before being destroyed by the intense heat and pressure (Venus, despite being home to heavenly-named locations such as Aphrodite Terra, is actually one very real Hell).
Almost as cool, in 2001 NASA got the NEAR Shoemaker probe to land on the asteroid 433 Eros, a manouver that wasn’t even in the flightplan. Crazy.