After a years-long journey, the Mars rover Opportunity is finally only a matter of feet from its highest-priority target at Endeavour crater, the phyllosilicate (clay) deposits which could reveal additional evidence for past water on the planet which was not too acidic or salty, a more benign environment for any possible life.
Opportunity is still on Cape York, the flat island-like plateau on the inner rim of Endeavour, but has now driven farther north, closer to where the clays deposits have been identified from orbit by the Mars Reconnaissance Orbiter. Interestingly, there is also a pattern of linear markings on the ground very close by, forming a sort of series of rectangles. Ancient ruins? Unfortunately probably not, as they closely resemble similar polygonal features on Earth and elsewhere on Mars which are known to be associated with clays, a natural geologic process. This would seem to confirm that Opportunity is now very close to its target. See the second set of images here in particular, as well as more detailed information.
There are also sulphate deposits here, which are similar to those seen previously up close by both rovers, and form in liquid water which is typically more acidic. The presence of both types of deposits in Endeavour will help to understand the history of water in the region, as it is generally believed that Mars went through periods of significant change early in its history, where the first bodies of liquid water were more neutral and non-acidic, followed by water that was acidic/salty before it was mostly lost in the thinning atmosphere and buried underground as vast ice deposits and possibly aquifers.