MIT student Christian Reed got bored this summer and spent his time doing something constructive: Building a homemade grappling hook launcher with a fire extinguisher. Amazingly, the device works really, really well. Rorschach from "The Watchman" would be proud. Check it out.

He explains his invention at Instructables

Although I call it a grappling hook launcher, it is basically a souped up version of any pneumatic gun.  I took the best aspects of many different spud guns to make one of the best possible systems doing my best to avert creating any weak spots and not using any dangerous PVC (which shatters when over pressured and does not work well in the cold).  This system is designed to be robust and efficient in every aspect of its construction.  It is not hard to build and the most trouble anyone would have is gathering all the materials needed.

I tried my best to used parts locally avaliable (Home Depot, Lowes, etc) but a few i needed to order online. Feel free to ask me any questions you may have. 
 

For everyones information, if you are really that concerned about why I didn't film myself climbing the rope,  you are missing the purpose of the video, to show you how it works.  The hook and rope combined for my gun weight 2lbs 2.1oz for anyone concerned that this device isnt practical.  Also, I launched the hook at 150 psi and you could go much higher to achieve greater heights. 

Hat Tip: IHC