This human-powered elevator is cool on many levels. First of all, this guy needed an elevator for his tree house! That, in my opinion, is a good problem to have. Secondly, his solution is elegant and fun.
From the video description:
I have built a tree house (though it is not finished yet) that is nearly 30 feet up a tree. I got tired of climbing a ladder six and a half million times a day, so I made a bicycle powered elevator to solve this problem. Don't you wish you had one?
He's counter-weighted the bicycle on the pulley system so less power is required to raise and lower the rider. Next, he has threaded a thin cable that runs around the bike's back wheel and up a tube in front of the rider. When the bike is pedaled in the forward direction, the bike "rides" up the cable. The weight of the rider and bike, keep the back wheel tight against the cable. This means he can also used the hand-brake on the bike's back wheel when descending, as you will see in the video. This is a beautiful bit of engineering and I wouldn't be surprised to see it used elsewhere in the years to come.
Here's a link to a post about the bike elevator on the Colossal blog.
[ Thanks Christoph!]