Railbikes are pretty self-explanatory. You take a bike, attach an extra wheel sidecar-style, jump on some railroad tracks, and ride. There's no need to steer, so you can look around as you pedal. You stick to abandoned railroad tracks so there's no surprises either. It's not a new idea, dating back well over 100 years to the first bikes, and recently even custom bike builders have devised their own versions. More at Flickr on the railbike tag and in the railbike group. There's even a book about it .
Cycling for a cause is the project/site of Canadian college student Michal Brichacek. On May 3rd of this year he set out from Alaska on his bike, aiming to ride all 12,000km (7440 miles) by early August. He's riding to raise money for the Lance Armstrong Foundation and he's over halfway done, currently riding across a hot Mexico landscape. His blog has his daily adventures (mostly about having to look for tent spots, supplies, and meeting interesting strangers). He's also posting daily photos of the trip.
The World Naked Bike Ride unfortunately took place yesterday, but is probably something worth doing next year. I imagine it's a lot like Critical Mass, with less driver anger and more rider embarrassment. Sounds like it was fun in Portland. (slightly NSFW photo on the front page of WNBR)