Gigapans

http://gigapan.org/gigapans/10660/

Here's an example, but there are a TON of different ones posted there, including a great many of Pittsburgh, different ML baseball stadiums, and at least several national parks(there's probably a bunch of those).

Use the mousewheel to zoom in and out, Left Mousebutton to grab and drag. Click on the small pics underneath to zoom to that location.

That is cool. Looking at all the people on the Brooklyn bridge taking photos.

I could have sworn that I responded to this post earlier........

It does look very cool and could be a big time sink for sure