Cruithne (3753 Cruithne) is in a near Earth orbit. Technically, a horseshoe orbit, because it orbits the sun so close to Earth's orbit that it almost, but never, passes us. When visible, which is rare, it appears to move in a horseshoe pattern.
It also crosses the orbits of Mars and Venus and even Mercury.
Why, if it is so close and so large (over a mile and a half) haven't we tried to probe this small world?