Oops, that was meant to be 'A Tiny Challenge' & 'A Medium Challenge', but the link is there for you anyway.

Hey, I only just saw your message on my Portal 2 screenshot. The map was called 'A Tiny Challenge' which you can find here - http://steamcommunity.com/sharedfiles/filedetails/?id=138131983 - and he also has another one called 'A Medium Challenge'. They're essentially race/puzzle maps, and one that you'll definitely want to do with a friend who hasn't done it before. They're pretty awesome! ^^

:P