As you get closer to the tree, you feel a sensation, best described as pinpricks of icy-hot, along your back and shoulders. A warm gust of wind blows, almost like the breath of a great creature. The sensation picks up as it does.
You too feel the sensation, but to a lesser degree. It's then that you feel something...off, just for a second, but then it's gone again. The feeling is akin to losing your balance, a split-second lurch that is there for a blink.
When you finally pass through the square of light, you are greeted by a blasted wasteland. Grassless dirt stretches onward, as far as the eye can see; rocks and rubble are strewn along. There is a faint, impish squeal on the wind, far in the distance and with a hint of chittering bats. A tempest brews above, lightning flashing through dark and sulphurous clouds, the wind stinking of brimstone and mold and rot. Far in the distance, you see the same great tree that rises aboveground, but this version of it lacks the patches of vegetation. In fact, it looks burnt and partially rotten.