It would be pretty great to fly close by over the ponderous 16th century castle of El Morro in San Juan, but it could be a pricey proposition, and you might garner some unwanted attention from Puerto Rican officials. Well, there is another option, and that is to take in El Morro (and many other world landmarks) via the National Geographic Magazine's Photosynth website. The site draws on technology developed by Microsoft, and essentially takes a large collection of photos, analyzes them for similarities, and stitches them together to create a rather fine immersive experience. Visitors are also welcome to submit their own photos for inclusion in this project, and landmarks currently under construction include Petra, the Sydney Opera House, and Seattle's Space Needle. Also, visitors will need to download the free Photosynth software to take full advantage of the site.