Please click on the images for larger viewing.
This image is Sol 894b from Opportunity Rover.... this one available from the Nasa site. Please note the sections missing from the image (black)
Now, here below is the same yet 3d version of the image from MSS, without any pieces missing!

Again here below, is the same 3d version of the image from MSS as mentioned just above, with just 3 areas of interest circled by me using Paint. Most obvious is the small rock bridge, very clearly visible and clearly a construction (not a natural phenomena). The circled marking to the left of the image surrounds a very definitive square in the ground as seen in the cut further down the page a little, with the marking to the right of the image displaying a very clear carving in the rock. Both cut from the 3d image and displayed below this 3d image.

Now there is very clearly a square in the ground as seen in the cut below, with what appears to be metal bordering, and what's that within it I wonder?

And here below, well there seems to be some clear carved rock work -

For very informative news on the situation at hand, and containing all Nasa images..... please visit -
http://www.marsanomalyresearch.com/index.htm
http://exopolitics.blogs.com/
http://secretofmars2.blogspot.com/