Apollo 13 was the 3rd attempt to land humans on the Moon and the 1st to fail. Fifty-six hours into the mission, an explosion forced the crew to abort their Moon landing and take shelter in the Lunar Module. The crew ultimately returned to Earth safely.
The two spacecraft currently orbiting the two innermost planets are both flying low in their orbits in the final phases of their missions. MESSENGER just performed a rocket burn to raise its orbit slightly, while Venus Express did the opposite.