10 maps. 0 buttons, 0 cubes, 0 turrets, 0 bridges, 0 funnels, 0 lasers, 0 faithplates, 0 stairs and 0 platforms. No gel, no glass, no grating and no water.
Just you and a portal gun. As well as distance, height, momentum and visibility. And a large number of tricky methods of combining them.
And you know what, I think these test chambers look even better than they did before. It was easy, really. You just have to look at things objectively, see what you don't need anymore, and trim out the fat.