According to this video, David Martines was looking around Google Mars when he happened to find a large building-like structure in the northern hemisphere of the planet. He calls it "Bio-Station Alpha," which of course is not its real name, but he assumes someone or something is living in it. Martines estimates that the white structure is over 700 feet long and 150 feet wide. It can be found at the following coordinates on Google Mars: 71 49'19.73"N 29 33'06.53"W
I checked this out in Google Mars myself and the thing is there at the coordinates given. Is it a structure? It sure looks like one. However, we must consider that even on Google Earth, the application is prone to anomalies here and there, showing "artifacts" that aren't really there. So that is a possibility.
Yet Google Mars is based on NASA satellite photos of the planet. If it is a structure, it appears to be in a good location for one -- what looks like a smooth, crater-free plain. What's needed is a high-resolution image of the site. What do you think?