I enjoy armchair space geocaching. Finding weird things people have found in NASA photos of Mars, and then trying to locate precise longitude/latitude for them in Google Earth (Mars).
It can be difficult because the tinfoil hat Mars buffs tend to rotate photos 180 or 90 degrees from Martian north without explanation, almost as if they don't want anyone duplicating their findings.
But anyway, there's this photo taken in 2008 by the Mars Reconnaissance Orbiter:
The Jet Propulsion Lab has these images as JPEGs, but they have much more detailed photos in .JP2 format, several hundred megabytes large.
It took me awhile to figure out how to view .JP2 files (Thanks, Steve and Jeff!). And the folks on the CosmoQuest forum.
IrfanView: http://www.irfanview.com/ Plugin for JP2: http://fileforum.betanews.com/detail/Ir
allowed me to zoom in on the .JP2 files.
There's a monolith on Mars (Yes, I know, it's a natural formation, but it's still cool)!
Posts on the web about it like this one:
I finally figured out it's in Google Earth (Mars) at roughly 7.233 S, 267.365 E. Or maybe just a little south of there.