http://a.imageshack.us/img198/8594/dscf0635d.jpg

it's on the driver side near the front. I'm trying to track down vacuum leaks as my idle is going nuts.

 

That looks like its going to the Cruise Control. If it is, then there should be a vacuum canister in the wheel well that the hose should be connected to. You will get to the canister by removing the fender liner. There should also be a grommet that its supposed to pass thru, which looks like its right next to the P/S pump gear in the pic

 

What Model prelude is this picture coming from? Enzo15 is right its some how connected to your cruise control but it looks cut (based on the pic) so good luck trying to get it to where it belongs cause it looks a little short to really go anywhere. But I don't know what model Prelude this belongs to so i'm not positive.

 

Its the cruise control vent dump tube. It vents into the atmospere. It vents into the body of the car through a grommet. Or you can just let it hang there.