On the last level of portal when you have to find gladis (sorry about spelling I don't know how to spell it) there are two areas where there are platforms rasied all the way up but one is rasied more than the others. It looks just like a white light but, if you use the put portals on any surface then you can shoot a portal up into there. When you get up into there time slows down and when you move the camera around there is colors like a rainbow or if you were on drugs. Make sure you save before you go up there because you can't come back down!
At two fort. If you are a very defensive player and you don't like playing in the front line or even if you are choose the enginer. You can either build a turret in the corrner of the intellengince room and stay their or build the turret their and try to get the enimies intellengince while the turret is protecting the intelligence. If a enemy spy puts a sapper on your turret tell the team the enime is in the intellengince room.