The highest ground in the solar system.
The summit of Olympus Mons is the single highest point on Mars — and in the entire solar system — rising 21.9 km (72,000 ft) above the planet's datum. So little air remains at this altitude that you stand above roughly 99% of the already-thin Martian atmosphere.
Claim your plot here →To reach this point you would climb a shield volcano so vast and so gently sloped that, standing on top, the horizon curves away below the base — you could not see the volcano's edge from its peak. At 21.9 km the summit towers about two and a half times higher than Mount Everest measured from sea level.
The air here is a near-vacuum. Mars's surface atmosphere is already less than 1% of Earth's, and by the summit almost all of that remaining gas lies beneath you. It is, in a very real sense, the closest you can stand to space while keeping your feet on solid ground anywhere in the solar system.
At 21.9 km it stands roughly 2.5 times higher than Everest's 8.85 km above sea level.
The summit rises far above the ~10 km altitude where airliners fly on Earth.
You would stand above about 99% of Mars's thin air — essentially on the edge of space.