Explore the wonders of solution caves, lava tubes, sea caves, and other underground realms at this beautifully illustrated Web site, developed by caver and photographer Dave Bunnell. The site features photographs of caves throughout the world and maps of idealized "virtual" caves, which explain and illustrate examples of nature's handiwork.Go to: http://www.goodearthgraphics.com/virtcave.html

Quantum physicist Eric J. Heller of Harvard University writes computer algorithms to convert scientific data into brilliantly colorful images. A selection of the resulting graphic images is now featured in an art exhibition titled Approaching Chaos. These Web links to Harvard Magazine and to Heller's own Web page highlight several of these intriguing artworks.Go to: http://www.harvard-magazine.com/archive/01jf/jf01_feat_quantumart.html and http://monsoon.harvard.edu/images-ejheller/

Check out an amazing, new information-dispensing device at the Web site of technology critic Langdon Winner of the Rensselaer Polytechnic Institute. Winner's Automatic Professor Machine delivers online doctoral degrees without the student ever having to set foot on a college campus. A spoof of the distance-learning craze, the site features a news report, radio interview transcript, recorded lecture, view of Glow-Ball University, and more.Go to: http://www.rpi.edu/~winner/apm1.html

Interested in computer history? Alex S. Pang of the Stanford University Library has assembled fascinating material from a variety of sources, including papers donated to the university from Apple's corporate library, to portray the invention and emergence of the Macintosh personal computer. The evolving Web site includes sections on counterculture and computing, the early Macintosh, the Apple mouse, technical documentation, marketing the Macintosh, and user groups.Go to: http://www-sul.stanford.edu/mac/

If you haven't really been paying attention for the last 450 million years or so of Earth's history, London's Natural History Museum offers a tidy way to catch up with a diverse, venerable group of marine invertebrates known as echinoids. Spectacular color images highlight important distinguishing characteristics of each type of sea urchin. Find out how sea urchins walk and how to sort out the pores on the underside of sand dollars.Go to: http://www.nhm.ac.uk/palaeontology/echinoids/

In the history of human flight, first came the daring tinkerers who gave wings to the pent-up human desire to soar. In the wake of their successes came a remarkable proliferation of flying machines, spacecraft, and colorful characters. At this Web site, the American Institute of Aeronautics and Astronautics celebrates these achievements with an annotated timeline of aviation history, brief biographies of famous pioneers, and a kids page presenting aircraft fundamentals and experiments.Go to: http://www.flight100.org/

Should anyone dismiss lichens as so much gray-green crust, send the detractor to the lichen glamour shots in this Web site's portrait gallery. The lush photography details shapes from goblets to anchors and colors from blue to neon Lycra-pants lemon. Other images illustrate the importance of lichens for other creatures (see the flying squirrel nest) and as environmental monitors (see the comparison shots of lichens on tree trunks in clean and polluted air).Go to: http://www.lichen.com/

Dracula doesn't want to suck your blood. He wants you to enter his online library and learn about the properties of light, waves, and particles. Here at "The Atoms Family" Web pages, created by the Miami Museum of Science, Dracula and four other silver-screen ghouls invite Web surfers into their laboratories to try out physics experiments geared to children from kindergarten to grade 12.Go to: http://www.miamisci.org/af/sln/index.html

Visit the e-Skeletons Project to take a close-up tour of the bones of a human, gorilla, and baboon. Visitors can compare selected bones of one species to those of another and can download plug-ins to view skeletons in 3D movies and images.Go to: http://www.eSkeletons.org/

The Web site of the Society for Amateur Scientists offers discussion forums, projects, and resources for people interested in taking part "in scientific adventures of all kinds."Go to: http://earth.thesphere.com/sas/ or http://www.sas.org/