NASA's Mars Curiosity rover will explore dark sand dunes on the Red Planet, some of which are as tall as a two-storey building and as broad as football fields.
No active dunes have been visited anywhere in the Solar System before, other than on Earth.
But that is about to change over the next few days, when the pioneering rover gets a close-up on the Bagnold Dunes - which skirt Mount Sharp.
So far, the rover has explored sand ripples and drifts, but not the much larger dunes. The dunes are active, moving around one metre each year.
NASA scientists want to know more about the dunes, and hope the information will help them to better understand the layer of sandstone on the planet.
As of Monday, the rover is about 200 metres away from 'Dune 1', and is currently monitoring wind direction and speed as it creeps closer.
Once it reaches the dunes it will start to scoop up samples and process them in its on-board laboratory instruments.
It will also use a wheel to scuff the dune to compare its surface to its interior.
Movement is a slow process for the rover - it has travelled a mere 315m in the past three weeks.
It is on a mission to discover how Mars' ancient wet environment changed to the harsh dry conditions we see today.
Nathan Bridges of Johns Hopkins University led the Curiosity team's planning for the dune campaign.
He said: "These dunes have a different texture from dunes on Earth. The ripples on them are much larger than ripples on top of dunes on Earth, and we don't know why. Now we'll have the first opportunity to make detailed observations."