Your longest fall? *Duh, spoilers*

[McGooTheWise]

I managed to get the 300 ft drop achievement very easily, as I sustained a fall for a good 10 minutes. In the room where the multi turret battle takes place in the end of the game, before you go meet GLaDOS, you can see that there are 2 opened panels that point upwards. Stand between these 2, and put a blue portal on the lower one, and place an orange one on the ground below you. As you fall do your best to keep the fall going. I noticed a patter when doing this. You fall once, then you fall in about the same spot, then you fly across the room, and brush the wall, place a portal directly beneath you. Then when you make it back through, you might fly at one of the pillars in the room. Place another portal where you are about to land. Now you will get high enough that you would land on the upper panel. Place an orange portal on this and fall back through. After 2 more portals you begin to see a pattern. I saw it as:

1. Close portal
2. Far portal (Placed beneath the player)
3. Panel portal

Rinse and repeat. Great fun if you're perpetually bored like I was.